fault and fold growth of the amenthes uplift implications for late noachian crustal rheology and heat flow on mars abstract determining the rheologic conditions that control growth of compressive structures on mars is an elusive problem one limited by the lack of seismologic and other data commonly available for comparable active uplifts on earth in some instances however the geometry of faults on mars that offset impact craters can be deduced from surface topography alone with this aim construction of a balanced and restorable structural cross section across the late noachian amenthes uplift or fault related fold suggest it forms above a deeply penetrating blind thrust with a gently curved or listric geometry that flattens downward preferred structural solutions suggest the thrust dips between 41 5 and 56 1 at the surface and flattens into a horizontal decollement at depths of 33 48 km the range of values for depth to detachment are greater than previous estimates for the amenthes thrust based on elastic modeling for a range of planar thrust geometries using the inference that the decollement corresponds to the onset of plasticity in the crust the depth to detachment is consistent with surface heat flow of 24 33 mw m 2 based on average values for heat production and the temperature threshold for the transition from brittle faulting to ductile shear on mars this suggests the crust at amenthes during the late noachian may be slightly cooler than previously thought similar to recent estimates derived from studies of lithospheric strength

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

levee morphology and sedimentology along the lower tuross river south eastern australia levees on the lower tuross river in south eastern australia reflect a complex interplay between depositional and erosional processes stream power conditioned primarily by valley width is the key determinant of levee morphology and sedimentology in this confined valley setting three styles of levee are described the rewlee levee is functionally linked to a flood channel in narrow valley settings 250 m these levees contain a diverse facies assemblage characterized by various scales of erosion surfaces vertical accretion on levees has produced conditions under which stream power values exceed the threshold for catastrophic floodplain stripping the levee at the mortfield site is associated with less confined settings valley width 500 600 m which present lower flood stage and stream power conditions this levee hosts a wide range of facies but erosion surfaces are seldom observed in the more open valley setting at the central site valley width 700 1000 m levees comprise uniform fine grained deposits which grade to pronounced distal floodplains with backswamps as levees reflect a combination of within channel and overbank processes both depositional and erosional these geomorphic features influence the character and sedimentology of adjacent landforms and the associated alluvial architecture of the basin

sources and occurrence of c12c22n alkane distributions with even carbon number preference in sedimentary environments abstract the occurrence of c12 c22n alkanes with a strong even carbon number preference is reported in recent and miocene sediments encompassing marine and freshwater systems deposited under oxic and anoxic conditions it is therefore shown that these n alkanes can be found in a wider type of sedimentary environment than those previously described the occurrence in some cases of a parallel distribution of c14 c20n alk 1 enes is also illustrated a variety of biological sources including both marine and freshwater bacteria as well as fungi and yeast species is suggested to account for such distributions

recent tectonics and subsidence on mars hints from aureum chaos article i nfo high spatial and spectral resolution imagery and topography collected during the last decade are changing our vision of mars into that of a geologically active planet even in recent times however the connection between internal activity such as faulting and other recent geomorphic processes and deposits such as eolian or mass wasting units is difficult to establish in this work we study a geomorphic feature located inside aureum chaos 4 s 333 e which is situated at the dichotomy boundary between southern highlands and northern low landsonmars weidentifiedfault relatedactivity basedonhiriseimagery andmappeda landslideof ltd light tonedeposits materialwhich seems to bemodifiedbya fault displacementmeasurements acrossthe scarpare in agreement with values measured in other amazonian aged extensional settings on mars moreover the rela tion between landslide and eolian material shows that it was produced very recently in time since the activity seems to postdate a dune field whose age was determined to be less than 1 9 myr old this observation together with other scarp related activity near the area suggests that very recent subsidence activity has occurred along previous fault planes inside aureum chaos

extension across tempe terra mars from measurements of fault scarp widths and deformed craters two independent methods with no common assumptions have been used to estimate the extension across the heavily deformed tempe terra province of the tharsis region of mars one method uses measurements of normal fault scarp width with average scarp slope data for simple grabens and rifts on mars to estimate the fault throw which combined with sparse fault dip data can be used to estimate extension formal uncertainties in this method are only slightly greater than those in other methods given that the total uncertainty is dominated by the likely uncertainty in the fault dip assumed to be 60 15 measurement of normal fault scarp widths along two n25 50 w directed traverses across tempe terra both yield about 22 16 km of extension or 2 strain across the northern traverse and nearly 3 across the southern one about three quarters of the extension has occurred during the two main phases of tharsis related deformation from middle late noachian to early hesperian and from late hesperian to early amazonian with more extension closer to the center of tharsis during the first phase extension across the region was also determined by measuring the elongation and elongation direction of all ancient noachian impact craters without ejecta blankets which predate most of the deformation results have been corrected for initial non circularity of craters established from similar measurements of young post deformation impact craters yielding a statistically significant mean strain of 1 96 0 35 in a n38 10 w direction across tempe terra extension of 20 4 comparable in magnitude and direction to the average result from the scarp measurement method both methods indicate an average extension for single normal fault scarps and shortening across wrinkle ridges for the crater method of 100 m the agreement between the results of the two independent methods in overall extension and average single normal fault extension argues that the average scarp slope and fault dip data in the fault scarp width method accurately represent the actual extension across the observed structures this conclusion supports existing geometric and kinematic models for structural features on mars a preliminary estimate of the total circumferential extension around tharsis at a radius of 2500 km is roughly 60 42 km total hoop strain is about 0 4 distributed heterogeneously tempe terra is the most highly strained region on mars

three dimensional normal faulting models of the valles marineris mars and geodynamic implications inversion of martian topography using a three dimensional boundary element model permits revised estimates of fault dip angle depth of faulting paleogeothermal gradient and extensional strain in the valles marineris region the major normal faults dip at 40 55 to depths of 60 75 km with comparatively small footwall uplifts 500 m for throws to 10 km implying that paleogeothermal gradients during faulting were 10 k km 1 or less assuming relatively rapid strain rates appropriate to the extending martian crust accumulation of dip slip offsets along the main normal faults likely was associated with anticlinal flexure and deformation of preexisting strata within the troughs the magnitudes of the predicted vertical and horizontal displacements outside the troughs as well as extensional strains are spatially variable depending on both cross and along strike position relative to the troughs the predicted displacements and strains attain maximum values at the troughs and decay to background values at cross strike distances of 250 km corresponding to 3 4 times the depth of faulting with an average province wide strain of 4 15 by implication the aggregate strain field surrounding tharsis is a highly variable spatial and temporal composite of the inhomogeneous strain fields each associated and scaling in size with an individual graben from the smallest structures through the largest valles marineris troughs

strained craters on ganymede high resolution images of jupiter s satellite ganymede obtained by the galileo spacecraft reveal several elliptical craters that are transected by sets of subparallel ridges and troughs oriented roughly orthogonal to the long axis of the crater implying that these craters have been extensionally strained we analyze five such craters four in the ancient dark terrain and one in bright grooved terrain inferring their strain histories by assuming each crater was originally circular these strained craters have been elongated by amounts ranging from 5 to 50 all are deformed by extension near perpendicular to subparallel ridges and troughs and some are also deformed by distributed simple shear parallel to these tectonic structures the rift zones that deform these craters show extensions of 5 up to 180 for a well defined fault zone that rifts saltu crater within dark terrain of nicholson regio extensional fault zones consisting of domino style normal faults and representing strains of several tens of percent may be common on ganymede and strains of this order can alter pre existing surface features beyond recognition through the process of tectonic resurfacing

quantitative analysis of the extensional tectonics of tharsis bulge mars geodynamic implications about 10 of the tharsis bulge surface is intensely faulted with a fault density up to 1 fault km in these intensely faulted areas 54 impact craters which exhibit faulted walls and floor are now elliptical in shape these ellipticities indicate an average strain value of 10 inside these provinces this strain value is 4 times greater than the strain deduced from normal fault morphometric analysis this high value indicates that the strain is not only due to 60 dip normal faults and that some additional tectonic processes exist such as boudinage this important strain value corresponds to an elongation of about 50 km across thaumasia and tempe mareotis provinces and 20 km across alba patera regio the amount of elongation for the entire tharsis region is 2 orders of magnitude higher than the strains and motions related to standard models of bulge formation these intensely faulted areas are restricted areas where faults are both radial to the bulge and perpendicular to the topographic slope the stretching does not influence the regional topography and there are no topographic shoulders or important level differences between faulted and nonfaulted areas which would indicate that the crust is not thinned under the stretched provinces outside these intensely faulted areas the graben width is remarkably constant all over the tharsis bulge indicating the existence of a brittle ductile transition or an incompetent level at about 1 2 km below the surface a new origin for the tharsis tectonic features is proposed as a preliminary hypothesis the intensely faulted areas correspond to the uphill parts and to denudation zones of gravity slidings which move on a 2km deep incompetent level the gliding of the slab on the very low dipping flanks of tharsis needs three conditions 1 the viscosity of the incompetent layer must be equal to the viscosity of the ice 2 the brittle layer must have been previously faulted by the bulging itself 3 these preexisting radial fault directions must be perpendicular to topographic slope the ridged plain units in lunae palus and coprates provinces thus correspond to a zone of blocking inside the gliding slab due to an interruption of the decollement level

morphometric and geometric characterization of normal faults on mars abstract using three different approaches fault plane fitting 3d crater rim palinspatic restorations and fault scarps morphometric analysis we investigate the geometry and degradation history of martian normal faults in two distinct areas the three independent methods produce similar results indicating that the average dip angle of the normal faults on these two locations is probably below the value that is usually assumed for mars 60 our best estimate for this average dip angle is 46 8 9 8 which is a value comparable with the mean dip angle inferred on earth for seismically active normal faults this lower average dip angle implies that all the rift strain estimates performed until now might be underestimated from the comparative analysis of the two faulted regions phlegethon catena and claritas fossae we show that local and regional dip variabilities may exist on mars this reinforces the idea that the amount of extension associated with martian rifts must be reconsidered we also demonstrate the advantages of performing a comparative morphometric analysis of fault scarps this approach enables the reconstruction of the faults scarps degradation history and can be used to evaluate how environmental conditions changed through time after modeling the degradation of the fault scarps at the two sites we conclude that the observed morphometric variations are mainly due to the different faulting ages in an environment characterized by low scarp degradation rates 4 10 3 m 2 kyr over the last 3 ga

mire development and environmental change barrington tops new south wales australia abstract sediments began accumulating in nine mires on barrington tops on the northern tablelands of new south wales before 11 000 yr b p and peat became common in the region by 8600 yr b p sedimentation rates were low but increased markedly about 3000 yr b p and again around 500 yr b p as a result of regional climatic change a comparison of the results with other environmental data from the region suggests that conditions in the early holocene were warmer and moister than at present but that cooler and drier environments developed about 3000 yr b p in the last 500 yr a slight warming and either increased precipitation or cloudiness has become evident

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

tectonic history of the tharsis region mars the faults of the tharsis region of mars have been mapped and delineated on the basis of age the orientation of each group of faults was analyzed to determine if they were radial to a point the results indicate that there are at least four discrete centers of faulting within the tharsis area which are of significantly different age the four centers proposed are from oldest to youngest 1 in the thaumasia highlands 2 in northern syria planum and finally 3 and 4 near pavonis mons while episodes 3 and 4 occupy the same geographic position they are separated in time by the development of the tharsis lava plains and shields each episode of tectonism was separated from the next by a period of major basaltic volcanism the tectonic features of the tharsis area are thus viewed as being the cumulative result of the superposition of several discrete episodes of faulting rather than the result of one episode about a single point

wrinkle ridges of arcadia planitia mars wrinkle ridges of arcadia planitia were examined to determine their morphology spatial distribution and the amount of crustal shortening and strain they accommodate ridges trend generally northward but their orientation and distribution are strongly controlled by the relief of the underlying knobby material ridges begin or end at inselbergs of older terrain and are associated with buried craters arcadia planitia ridges have an average width of 3425 m and accommodate an average folding shortening of 3 m and a faulting shortening of 55 m mean total shortening is 57 m three east west transects were constructed at 20 25 and 28 n to estimate regional shortening and strain average total shortening across the transects is about 900 m corresponding to a regional compressive strain of 0 06 the total shortening and compression across arcadia planitia are less than in lunae planum faults associated with the arcadia ridges are inferred to have a westward dip compared with an eastward dip for lunae planum ridges the generally levels of compression and symmetric orientation of the ridges suggest a regionally organized stress system differences in the shortening and strain between lunae planum and arcadia planitia may reflect the effects of local lithology or azimuthal variations in the stress field

peculiarities of salt lake sediments as potential source rocks in china abstract hypersaline lake sediments are widely distributed in china and can be good sources for petroleum the palaeogene sediments of the jianghan basin in eastern china are a typical example composed of salt lake evaporite clastic facies in fault subsided basins their organic matter is variable but is dominated by type ii kerogen the biological marker characteristics of core extracts and oils from the jianghan basin include i low oep values for n alkanes and occasionally an even odd predominance ii a high concentration of phytane iii a relatively high gammacerane 17 h 21 h hopane ratio and iv abundant mainly nickel porphyrins sample guang 33 k 33 is typical of the immature oils found in the jianghan basin geological and geochemical data both indicate that it was generated from source rocks in the maturity range r 0 0 45 0 55 its characteristics are similar to those of immature source rocks with high concentrations of phytane steranes triterpanes and nickel porphyrins and for an oil extremely low values for molecular parameters of maturity such as c 29 20s 20s 20r 14 h 17 h steranes c 32 22s 22s 22r 17 h 21 h hopanes and dpep dpep etio porphyrins

strength of faults on mars from mola topography the stresses which must be maintained on faults bounding the rift topography at tempe fossae the north tempe rift ntr and valles marineris vm on mars are estimated using a simple elastic model and topographic data from the mars orbiter laser altimeter mola the absence of rift flank uplift at the ntr is consistent with an elastic thickness te of 20 km or greater at the time of rift formation the maximum resolved shear stresses on bounding faults due to this topography do not therefore exceed 20 mpa similar to the inferred strength of terrestrial faults elastic thickness estimates at vm are mostly around 50 km or greater therefore for canyon widths of 400 km the bounding faults of vm if present must be able to withstand stresses of up to approximately 100 mpa however if the fault controlled sections of the canyons do not exceed 150 km in width as suggested by geomorphological analysis the fault strength required is only 20 mpa although the maximum resolved shear stresses required to support the topography at vm may need to be greater than the stresses which terrestrial faults can support at least some faults on mars are no stronger than similar features on earth this observation is consistent with the existence of liquid water in the shallow subsurface of mars at the time the faults were active on venus plate tectonics is probably prevented by the frictional resistance to motion across strong faults on mars it is more likely that the large thickness of the elastic layer of the lithosphere and the possible positive buoyancy of the crust are responsible for the observed lack of plate tectonics c 2002 elsevier science usa

late quaternary changes in carbon cycling on mt kenya east africa an overview of the δ13c record in lacustrine organic matter abstract the 13 c signature of sedimentary organic matter acts as a tracer for past changes in the terrestrial and aquatic carbon cycles compound specific 13 c analysis enables these two signals to be disentangled we compare the molecular isotopic records from a transect of five lakes between 1820 and 4595 m a s l on mt kenya east africa spanning the last 100 000 years with multiproxy palaeoenvironmental data in order to determine the mechanisms underlying late quaternary variations in carbon cycling at different altitudes the amplitude of down core variations in the 13 c values of total organic carbon varied from 4 8 to 17 4 the 13 c signals in compounds of terrestrial aquatic macrophyte and algal origin were tightly coupled reflecting strong atmospheric control during the early glacial and the last glacial maximum the effects of sub ambient co 2 and enhanced moisture stress reinforced each other resulting in carbon starvation and very high 13 c values in contrast smaller millennial scale shifts in 13 c during the late glacial and holocene were driven primarily by fluctuations in monsoon precipitation however the impact of late quaternary atmospheric changes were complex involving variations in biomass burning vegetation cover soil erosion lake levels and water chemistry in addition to direct physiological responses by higher plants and algae

the tempe volcanic province of mars and comparisons with the snake river plains of idaho abstract the tempe volcanic province of mars is a broad region adjacent to and superimposed upon the western tempe mareotis plateau the volcanic region is a relatively low plain of probable basaltic flood lava affinity superimposed upon this plain are a variety of small constructional and nonconstructional volcanic features all of which appear structurally controlled along an orientation of approximately n60 e constructional features included low shields composite cones and low irregular hills which may be silicic domes the nonconstructional features include linear depressions which may be rift zones fissure flows and pit craters the tempe volcanic province appears comparable in many aspects to features of the snake river plains of idaho while the tempe region may cover a significantly larger area than the snake river plains the same type and scale of features are observed on both areas the tempe region includes three styles of volcanism flood basalts a capping of fissure and vent fed flows with scattered low shields and areas where low shields have coalesced into plains type volcanism the snake river plains are represented by one style plains volcanism this represents one of the few examples where direct comparison can be made between martian and terrestial geologic geomorphic features and where a scale problem is not encountered

graben and extension in northern tharsis mars a morphometric analysis of north south trending graben at 35 n in northern tharsis is used to provide the first quantitative measurements of crustal extension in and strain for areas of the martian crust that have undergone both extreme and mild deformation these estimates also demonstrate the viability of the viking data for making such quantitative assessment graben in the region accommodate 8 km of post early amazonian east west extension this extension corresponds to a net regional strain of 0 45 0 61 local strains vary from 1 to 5 extension is nonuniform and localized near 110 south of alba patera and north of ceraunius fossae because of reactivation of preexisting fractures in underlying basement and possibly due to superposition of stress fields from tharsis and alba patera a major mechanical discontinuity in the shallow crust probably representing the base of or a strength contrast within the megaregolith is observed it occurs at a depth of 2 km on the profile flanks and is depressed to about 7 5 km near 110 due to loading of the crust by the volcano a number of more shallow discontinuities occur within the construct and probably represent lithologic contacts

discontinuities in the shallow martian crust at lunae syria and sinai plana detailed photoclinometric profiles across 125 erosional features and 141 grabens in the western equatorial region of mars indicate the presence of three discontinuities within the shallow crust pits troughs and wall valleys tributary canyons within noctis labyrinthus and valles marineris and escarpments within the fretted terrain of sacra fossae and kasei valles show distinct erosional base levels at depths of 0 3 0 6 km 1 km and 2 3 km the shallowest discontinuity corresponds to thickness estimates for the ridged plains unit in this region and thus the discontinuity probably is the contact between a sequence of layered rock making up this unit and the underlying megaregolith the 1 km discontinuity is reflected in the base levels of erosion of all the features studied and it may correspond to the base of the proposed layer of ground ice model calculations using photoclinometric profiles of simple grabens corrected for the effects of mass wasting and the 60 dip of bounding faults measured from the exposed traces of faults on trough walls show that graben bounding faults consistently intersect at the mechanical discontinuity at about 1 km depth this discontinuity may represent an interface between ice laden and dry regolith ice laden and water laden regolith or pristine and cemented regolith a correlation between wall valley head depth and local thickness of the faulted layer suggests that the 1 km discontinuity also controlled the depth of the heads of sapping canyons there is no apparent relation between the pit and trough depths and the local thickness of the faulted layer which can be explained if pits and troughs developed by subsidence into underlying tension cracks that disrupted the 1 km discontinuity the data do suggest however that erosion of shallow pits and troughs was influenced by the 1 km discontinuity the third discontinuity at a depth of 2 3 km corresponds to the proposed base of the martian megaregolith and is probably the interface between overlying ejected breccia and in situ fractured basement rocks

possible algal origin of long chain odd n alkanes in immature sediments as revealed by distributions and carbon isotope ratios a pliocene oil shale pula hungary a c3 plant triticum aestivum and a c4 plant zea mays were compared using isotopic composition of bulk organic matter along with distributions and individual carbon isotope ratios of n alkanes from organic extracts the microalga botryococcus braunii a race was thus shown to be the main source of the predominant 27 29 and 31 n alkanes of pula sediment therefore the dominance of odd carbon numbered n alkanes in the range c25 35 in extracts from immature sediments shall not be systematically assigned to higher plant contribution but algal input is also possible in fact the long chain n alkanes with an odd predominance previously observed in extracts of various immature sediments are likely to be derived at least partially from algae

paleohydrology of an upper aptian lacustrine system from northeastern brazil integration of facies and isotopic geochemistry abstract the codo formation records the initial evolutionary stages of an intracontinental rift system formed along the brazilian equatorial margin in the late aptian deposits of this unit exposed on the eastern margin of the grajau basin include gypsum bituminous black shales and limestones these lithologies were formed in a low energy well stratified anoxic and hypersaline lake system developed in a dominantly arid semi arid climate this lacustrine succession is internally organized into three categories of shallowing upward cycles with the first and second order cycles being related to seismic activity associated with fault reactivations and the third order cycles recording climatic fluctuations studies emphasizing petrography and analysis of the geochemical tracers fe mg sr mn na and ca helped to identify the sedimentary facies that kept a primary signal which were thus appropriate for isotopic investigations aiming paleoenvironmental and paleohydrologic reconstructions the results of this study revealed a wide distribution of dominantly low carbon and oxygen isotope values in carbonates ranging from 5 69 to 13 02 and from 2 71 to 10 80 respectively this paper demonstrates that at least in the particular case of oxygen the isotope ratios vary according to seismically induced shallowing upward cycles with values in general lower at their bases where central lake deposits dominate and progressively higher upward where marginal lake deposits are more widespread in addition to confirming a depositional signature for the analysed samples this behavior allowed the development of a seismic induced isotope model the lighter isotope ratios appear to be related to flooding events promoted by subsidence which resulted in the development of a perennial lake system while heavier isotope values are related to ephemeral lake phases favored by uplift and or increased stability furthermore the results show that a closed lake system dominated as indicated by the overall good positive covariance i e 0 42 to 0 43 between the carbon and oxygen isotopes though open phases are also recorded by negative covariance values of 0 36 during closed phases the 18 o displayed the highest range of variation i e 3 63 to 4 89 due to increased residence time while this variation was low i e 0 09 to 1 87 during open lake phases when there was a balance in the water isotope composition maintained by continuous basin inflow

assessment of downstream trends in channel gradient total and specific stream power a gis approach geographic information systems gis analyses of digital elevation models dems coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient total stream power and in riverscapes conducive to regime analysis also specific stream power for a small high relief coastal catchment in se australia good agreement was obtained between channel gradients derived from a 25 m cell size dem and field survey equivalents over distances of several kilometres indicating that channel gradients derived from dems can have a reasonable degree of absolute as well as relative accuracy over multi kilometre reach scales assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream modelling of downstream trends in channel gradient total and specific stream power from catchment wide dems has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient stream power and the form and dynamics of river systems

topographic analysis of devana chasma venus implications for rift system segmentation and propagation abstract devana chasma is a rift system on venus formed in association with the beta regio and phoebe regio volcanic highlands which are interpreted as mantle plumes we present a new analysis of a 2500 km long segment of devana based on the rift topography the horizontal extension across the rift boundary faults is 3 9 km this is a lower bound on the total rift extension because the altimetry does not resolve the topographic relief across the numerous faults that are visible in radar images of the rift floor the total extension across devana is approximately 20 km similar in magnitude to continental rift systems on earth rift flank elevations are up to 3 1 km in the regions nearest the mantle plumes and decay strongly with increasing distance from the plumes indicating a strong thermal component to the rift flank topography unlike the situation usually reported for terrestrial rifts as on earth there is also a flexural uplift component to the flank topography rift depths are up to 2 5 km below the surrounding plains with considerable along strike variability there is a 600 km lateral offset along devana chasma near the mid point between the two mantle plumes devana most likely formed as two distinct rifts due to the horizontal stresses created by outflow from the upwelling plumes the offset zone formed as a result of the interaction between the two rift tips which requires that upwelling at the two mantle plumes overlapped in time

resurfacing history of tempe terra and surroundings the resurfacing history of the tempe terra region is determined using the neukum and hiller technique of breaking cumulative frequency curves into separate branches where the curves depart from a standard production curve we find four surfaces recorded in the heavily cratered portions of tempe terra with crater retention ages n 1 242 100 95 700 20 800 and 5 500 this is interpreted to indicate three major resurfacing events occurred in this region ending at n 1 95 700 20 800 and 5 500 the ridged plains on the tempe terra plateau have an oldest recorded surface age of 20 400 identical to that of the second resurfacing event recorded in the heavily cratered areas a single resurfacing of the ridged plains which may have been a second episode of ridged plains volcanism occurred at n 1 7 800 the knobby plains to the north west and east of tempe terra also show a resurfacing at 20 000 and additional events at 5 400 and perhaps 1 600 mottled plains to the northeast record surfaces with crater retention age 7 500 5 000 and 3 900 where the first age is determined by a single surviving crater it appears that the lunae planum age lpa at n 1 20 000 resurfacing event seen elsewhere onmore mars was widespread and effective in this region a second widespread event appears to have ended at n 1 5 000 the authors estimate the thickness of the resurfacing materials corresponding to the lpa event to be less than 90 m in the heavily cratered areas but 300 500 m in the ridged plains themselves later resurfacing materials were generally thicker farther north in the mottled plains 300 m than in the knobby plains 200 m less

crustal extension in the ceraunius fossae northern tharsis region mars 1 we investigated the ceraunius fossae area northern tharsis in order to obtain quantitative information on the tectonic extension affecting this area tectonic structures of the ceraunius fossae area have been previously described using viking images and interpreted as extensional structures laser altimetry data mola can be used to quantitatively investigate these structures with a better resolution we developed a method to obtain e w oriented profiles perpendicular to the main tectonic structures with a sufficiently high resolution to analyze tectonic structures in spite of the low data density in this direction we interpreted all the recognizable extensional structures along the profiles and using a simplified structural model we estimated tectonic extension along these transects the extension calculated over the entire profiles is 36 km e24 l1 l0 l0 910 km 874 km 874 km 0 041 and 42 km e26 730 km 688 km 688 km 0 061 along profile 24 and profile 26 respectively in the most deformed area extension reaches the value of 22 km emax l1 l0 l0 186 km 164 km 164 km 0 134 since the extension accounted by the topographic doming is negligible a significant horizontal crustal motion is required to explain the observed extension

topographically associated but chronologically disjunct late quaternary floodplains and terraces in a partly confined valley south eastern australia the bellinger river catchment in the new england fold belt on the mid north coast of new south wales is characterized by an assemblage of stepped late quaternary alluvial units late pleistocene terraces were formed by large more competent rivers that eroded almost entire valley floors however a decline in discharge prior to the holocene has resulted in the abandonment of these deposits as elevated terraces or residual alluvium onlapped by contemporary floodplains intrinsic controls on floodplain formation appear to be superimposed over an early mid holocene climatic signature a fluvially active period known as the nambucca phase from 10 to 4 5 ka eroded late pleistocene terraces two floodplain surfaces one higher than the other both started to accrete vertically from 4 ka but with some valley locations remaining vulnerable to episodes of erosion resulting in substantial units of even younger basal alluvium the high floodplain is dominated by horizontally laminated vertically accreted sequences while the low floodplain which overlaps in age is characterized by pronounced cut and fill stratigraphy terraces and floodplains in partly confined settings can have similar elevations but be polycyclic with very different basal ages in such landscapes the classical assumption that individual terrace or floodplain profiles along a valley represent periods of coeval formation is shown to be frequently invalid copyright 2007 john wiley sons ltd

tempe fossae mars a planetary analogon to a terrestrial continental rift tempe terra the northeastern part of the tharsis region on mars is characterized by several extensional structures differing in style and age the tempe fossae a particularly well developed system of graben striking n45 e have been studied for the first time in detail on the basis of viking orbiter imagery and mars observer laser altimeter mola topographic data the graben system appears to be unique in the whole region because of its extent the remarkable width and depth of the graben the varying graben pattern and the associated volcanism single graben can be up to 35 km wide and 120 km long while their depth can reach nearly 3000 m they typically show an asymmetric architecture often in halfgraben or step fault style the graben system widens and changes its style along strike from ne to sw from a single very deep and narrow graben to a complex set of several shallower sinuous graben and halfgraben crustal extension was measured in the northeastern part from the observable throw and amounts to 2 5 3 1 km volcanic structures can be found at several locations along the graben in the sw the graben system seems to be connected with the tempe terra volcanic province marked by flood basalts and plains volcanism craters were counted on volcanic units unaffected by extensional tectonics crater statistics indicate an absolute crater model age for the upper end of the extensional deformation of 3 5 ga the dimensions and the characteristics of the mapped graben system resemble those of terrestrial continental rifts and a comparison between them and the kenya rift reveals striking similarities therefore the tempe fossae are interpreted as a martian analog to a continental rift associated with an underlying mantle plume this hypothesis seems to be supported by recent geophysical models based on topography and gravity data from mars global surveyor which indicate regional uplift for tempe terra

botryococcane in a new class of australian non marine crude oils there are few documented examples of source specific hydrocarbons in non marine petroleum and most of these are related to land plant precursors1 3 one such biological marker of algal origin is botryococcane c34h70 a geologically rare acyclic alkane derived from the freshwater green alga botryococcus braunii4 5 first discovered in several sumatran crude oils6 7 and here identified in a suite of coastal bitumens from 10 different stranding sites between kingston south australia and portland victoria table 1 figs 1 2 biological marker and carbon isotope analyses of these bitumens provide evidence for a new class of australian non marine crude oils the bitumens are inspissated waxy residues of paraffinic and paraffinic naphthenic crude oils that emanate from submarine seeps in the western otway basin8 12 and are characterized by high concentrations of botryococcane unlike other high wax australian oils13 14 the coastal bitumens contain up to 2 6 sulphur and seem to be primarily of algal origin their geochemistry can be used to predict the occurrence of extensive organic rich source beds that were deposited in deep meromictic lakes along australia s southern continental margin

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

organic geochemical characterisation of depositional palaeoenvironments of source rocks and oils in brazilian marginal basins abstract an investigation of bulk isotopic and molecular features of a wide selection of source rocks and oils from brazilian marginal basins ranging from lower cretaceous to tertiary in age provides a number of organic geochemical criteria that characterise and distinguish their depositional palaeo environments the methods employed include evaluation of organic carbon contents rock eval pyrolysis vitrinite reflectance measurements determination of carbon isotope ratios elemental and visual kerogen analysis assessment of oils and solvent extracts by liquid and gas chromatography and quantitative biological marker investigations using gc ms for aliphatic hydrocarbons and uv vis spectrophotometry for metalloporphyrins selected data were evaluated using principal component analysis the results enable the recognition and differentiation of seven depositional regimes lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate marine deltaic marine highly anoxic with a predominance of calcareous mudstone lithology and marine anoxic with predominance of siliciclastic lithology diagnostic features in the biological markers from these depositional environments include the carbon number distributions of n alkanes pristane phytane ratios absolute concentrations of carotane higher acyclic isoprenoids c 30 hopane and steranes and the abundance of the latter relative to 4 methylsteranes the occurrence and abundance of particular biological markers such as gammacerane tricyclic and tetracyclic terpanes 18 h oleanane 28 30 bisnorhopane and 25 28 30 trisnorhopane and the relative abundances of nickel and vanadyl porphyrins

application of biological markers in the recognition of palaeohypersaline environments the hydrocarbon fractions of a marl sample from a messinian basin in the northern appenines and four oils rozel point oil utah and three seep oils from sicily were studied

holocene palaeoecology and formation of the shoalhaven river deltaic estuarine plains southeast australia the shoalhaven river is one of the largest rivers on the south coast of new south wales and the deltaic estuarine plains associated with its mouth represent a mature stage of infill of a barrier estuary the stratigraphy of sediments from more than 60 drillholes from the plains indicates that the area has infilled during the mid holocene as a result of input of marine sands associated with a sand barrier on the high energy coast and fluvial mud and sands from the shoalhaven river molluscan assemblages indicate that marine influence was initially widespread throughout the eastern and southern parts of the embayment and that most of the plains infilled under estuarine conditions prominent levees across the plains surface are interpreted to be part of a birdsfoot delta distributary complex and individual floodbasins accreted progressively as they were encapsulated by distributary extension these former tidal environments mean that there are extensive potential acid sulphate soil conditions beneath the

late crustal growth on mars evidence from lithospheric extension 1 we apply the pure shear model of lithospheric extension to rifting on mars and investigate the range of initial ambient conditions that allow for narrow rifting the results are applied to the coracis fossae constraining the crustal thickness at the time the rift formed we thus find that the crustal thickness at 3 5 3 9 gyr is unlikely to have exceeded 50 km this is significantly lower than the estimates for the present day crustal thickness in that region 70 km and interpreted as an indication for continued crustal production at that time

late quaternary river evolution of floodplain pockets along mulloon creek new south wales australia valley confinement along upper middle reaches of mulloon creek in the upper shoalhaven catchment of southern new south wales australia restricts floodplain development to a series of distinct pockets these pockets comprise a downstream thinning wedge of vertically accreted fine grained deposits atop basal gravels some time before 12500 years ago a bedload dominated river was transformed into a suspended load system in the mid late holocene swamps developed in the middle lower part of each floodplain pocket within a few decades of european settlement of this region circa ad 1820 discontinuous watercourses in some floodplain pockets had incised to form a low sinuosity gravel bed channel wedge shaped units of post incisional alluvium that thicken downstream overlie the swamp and floodplain deposits in the downstream part of these pockets in the downstream most pocket incision commenced prior to colonization while upstream swamps retain a continuous swamp across the valley floor the late quaternary evolution of this variant of discontinuous watercourse is summarized in a schematic model

development of microbial carbonates in the lower cretaceous codo formation north east brazil implications for interpretation of microbialite facies associations and palaeoenvironmental conditions the study of microbial carbonates has acquired new significance with the recognition that they retain valuable information related to biomineralization processes associated with microbial activity throughout geological time additionally microbialites have a demonstrated economic potential to serve as excellent hydrocarbon reservoirs the lower cretaceous codo formation located in the parnaiba basin of north east brazil comprises a unique stratigraphic sequence of up to 20 m thick well preserved carbonate microbialites deposited in a continental basin during the initial break up and separation of south america from africa in the early cretaceous this lacustrine carbonate sequence provides an excellent example to investigate the palaeoenvironmental conditions controlling microbialite facies development based on macroscopic and microscopic observations of outcrop and drill core samples four microbialite facies stromatolite lamina massive and spherulite were defined and distinguished by textures and microbial fossil content changes in facies type are related to alternating palaeo water depths as reflected by 87sr 86sr cycles resulting from fluctuations in the sources of meteoric water clumped isotope measurements of stromatolitic fabrics yield precipitation palaeo temperatures with an average value of 35 c the 18 o values of bulk carbonate 6 8 to 1 5 vienna pee dee belemnite imply precipitation from water with calculated 18 o values between 1 6 and 1 8 vienna standard mean ocean water reflecting precipitation from variably modified meteoric waters the 13 c values of bulk carbonate 15 5 to 7 2 vienna pee dee belemnite indicate a significant input of carbon derived from aerobic or anaerobic respiration of organic matter combined the data indicate that the evolution of the codo formation occurred in a closed lacustrine palaeoenvironment with alternating episodes of contracting and expanding lake levels which led to the development of specific microbialite facies associations the results provide new insights into palaeoenvironmental settings biogenicity and early diagenetic processes involved in the formation of ancient carbonate microbialites and by extension improve the knowledge of the reservoir geology of correlative units in deep waters offshore brazil

anthropogenic influences on hydrocarbon contents of sediments deposited in eastern lake ontario since 1800 the amounts and types of extractable hydrocarbon components in sediment cores from the rochester basin of eastern lake ontario provide a record of environmental changes that have accompanied the settlement and population growth of the surrounding land areas sediments deposited prior to the mid 1800s contain low concentrations of hydrocarbons that are dominated by land plant wax components concentrations begin to rise in the late 1800s as erosion of soil and nutrients from watershed areas accelerated this pattern continues into modern times episodes of enhanced aquatic productivity are sometimes recorded in twentieth century sediments by the dominance of algal hydrocarbons but land plant components typically predominate petroleum residues begin to appear in sediments deposited in the late 1800 s but remain minor constituents of the hydrocarbon contents of modern sediments in the rochester basin

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

evaluating source rock organofacies and paleodepositional environments using bulk rock compositional data and pristane phytane ratios abstract insights into source rock paleodepositional settings and organofacies trends are critical to understanding basic expulsion characteristics of a source rock there is often a need to leverage disparate datasets using various proposed correlations in order to build a most likely plausible geologic scenario that honors the majority of the available information however it is not always clear how reliable are some of these correlations are as most source rocks intervals represent millions of years and have appreciable vertical and lateral variability a geographically large and varied organofacies dataset is used to test the very commonly used depositional environment indicator pristane phytane pr ph and a method based on x ray diffraction xrd data both of these disparate data types are increasingly available in the public domain and the results show these data can be used quickly and effectively to evaluate paleodepositional environments and organofacies overall it was found that historically used pr ph ratio cut offs are in agreement with independently derived organofacies interpretations roughly 90 of the time and the xrd based method agreement rate is approximately 80 the two techniques were also in good agreement when evaluated together on a coincident dataset however the correlations were not always straightforward and multiple lines of evidence and larger datasets are always recommended to support any interpretation in the xrd dataset carbonate percentages were the best differentiator of marine environments carbonate versus siliciclastic and clay percentages can be used to help separate terrigenous environments certain depositional settings lacustrine environments in particular also have more inherent variably that often require more geological evidence to constrain the interpretation beyond biomarker and compositional information

application of organic facies and biomarkers in characterization of paleoenvironmental conditions and maturity of sediments from the codo formation in the west central part of the sao luis basin brazil abstract paleoenvironmental conditions of the sediments of the cretaceous codo formation in brazil are still being debated the main point of controversy is whether they were deposited in a strictly marine environment or under lacustrine conditions of varying salinity in this study organic facies and biomarker analyses were performed on samples from the codo formation in the sao luis basin northwest brazil to reconstruct the paleoenvironmental conditions the origin and the thermal maturity of the organic matter four types of palynofacies associations pi amorphous organic matter pii amorphous organic matter sporomorphs piii phytoclasts and iv marine palynomorphs were identified the total organic carbon toc content exhibits a strong correlation 0 75 p 80 the thermal maturity indicators including vitrinite reflectance ro spore color index sci ts ts tm ratios and c29 20s 20s 20r and c29 indicate that the organic matter is immature to marginally mature

faulted craters as indicators for thrust motions on mercury craters cross cut by faults are used as markers to obtain fault geometric and kinematic properties assumingthattheshapeofthesecraterswasoriginallycircular itispossibletomeasure the horizontal and vertical components of fault displacement as well as the slip trend by applying trigonometric relations slip plunge displacement magnitude fault true dip and fault rake can be derived from the observed values an example application of this method on craters faulted by lobate scarps on mercury shows that most of these inferred reverse faults have moderate oblique slip trends moreover the derived dips of thrusts vary over a wide range of angles some preliminary results in terms of fault rake compared with fault dip strike and latitude are pre sented together with a pilot study to test and discriminate global tectonic models suggested for the evolution of mercury the possibility of estimating quantitative fault parameters through remotely sensed data provides significant assistance in the structural characterization of faults on planetary surfaces

structural modeling of lobate scarps in the nw margin of argyre impact basin mars abstract martian lobate scarps are prominent tectonic structures interpreted to be the topographic expression of large thrust faults generated under compression here we present a structural modeling performed on three large lobate scarps ogygis rupes bosporos rupes and phrixi rupes located in the heavily cratered highlands of mars specifically in aonia terra between thaumasia montes and argyre impact basin these lobate scarps formed in the late noachian early hesperian strike parallel to the edge of the thaumasia montes and were generated by ese vergent thrust faults structural analysis of craters deformed by these lobate scarps gives minimum estimates for the faults slip of 1700 3100 m we applied two structural methods in order to constrain the geometry of these thrust faults at depth area balanced cross sections and forward mechanical dislocation modeling obtaining a depth of faulting in this area between 18 and 45 km and dip angles between 23 and 35 these results are consistent with previous studies of lobate scarps on mars the depth of faulting gives an estimation of the depth of the brittle ductile transition at the time of its formation giving a range of depth in which the state of the lithosphere change from brittle to ductile dominated deformation the heat flow values calculated from the obtained depths of the brittle ductile transition range from 25 to 51 mw m 2 we show that the brittle ductile transition depth in aonia terra is set in 18 27 km at a larger distance from the basin center while it is deeper closer to the argyre rim 33 45 km this difference seems to indicate a thickening of the brittle domain under argyre main rim with respect to the external area but attending to regional geology and heat flow values calculated this high value 33 45 km might be an overestimation of the depth of faulting caused by the presence of the crater rim elevation before the formation of the lobate scarps

strain at radially fractured centers on venus 1 radially fractured centers rfcs on venus are distinctive 100 km long radiating systems of graben fissures and fractures arranged around a central topographic high we use cycle 1 and cycle 3 magellan images to determine the depths and wall dip angles of several large radial graben using two different methods at four rfcs becuma mons didilia corona h uraru corona and pavlova corona we record graben depths of 0 3 0 9 km and mean wall dip angles of about 36 which we interpret as a primary talus slope rather than a fault plane using the calculated depths and a more realistic fault dip of 60 we find extension of between 0 5 and 1 km on graben between about 5 and 10 km wide we use this extension to estimate the hoop strain at each rfc maximum measured strains on the flanks are typically between 1 and 4 and may be up to 7 toward the center we conclude that this strain is too large to be explained by current plume related uplift models and also by magma chamber inflation we conclude that dikes are probably responsible for the majority of the strain at the large radial graben

acheron fossae mars tectonic rifting volcanism and implications for lithospheric thickness 1 the acheron fossae region is an ancient crustal block exposed in the northwestern tharsis province on mars it is named after the acheron fossae a particularly well developed system of extensional tectonic grabens this study is the first to describe the tectonic inventory in detail using topographic and image data from the global surveyor and mars express missions we see the extensional tectonics along the east west trending topographic high of acheron fossae as a surface expression of upwelling asthenospheric material that initiated regional uplift crustal extension and breakup and associated volcanic activity in noachian time the tectonic architecture and the dimensions of the extensional structures are comparable to those of terrestrial continental rifts an area of elevated topography and strong erosion which constitutes a regional landmark in the eastern acheron fossae region is interpreted as a rift related center of volcanism caused by local magmatic uprise and involvement of the lithosphere the extension across the acheron fossae reaches values between 1 2 km and 8 7 km comparable to young continental rifts on earth crater statistics indicate an absolute cratering model age between 3 9 ga and 3 7 ga for the rifting the uplift observed on the flanks of the acheron fossae indicates a fairly thin and thus hot lithosphere using flexural analysis we have constrained the elastic lithosphere thickness at the time of rifting to 8 9 11 3 km corresponding to thermal gradients between 28 and 41 k km 1 these heat flows are substantially larger than noachian heat flow values previously reported but are consistent with the presence of rift related volcanism and a magmatically very active environment

morphological mapping of ganymede investigating the role of strike slip tectonics in the evolution of terrain types abstract the heavily fractured surface of ganymede displays many morphologically distinctive regions of inferred distributed shear and strike slip faulting that may be important to the structural development of its surface to better understand the role of strike slip tectonism in shaping this complex icy surface we perform detailed mapping at nine sites using galileo and voyager imagery noting key examples of strike slip morphologies where present these four morphological indicators are en echelon structures strike slip duplexes laterally offset pre existing features and possible strained craters we map sites of both light grooved terrain nun sulci dardanus sulcus tiamat sulcus uruk sulcus and arbela sulcus and terrains that are transitional from dark to light terrains nippur and philus sulci byblus sulcus anshar sulcus and the transitional terrain of northern marius regio at least one if not more of the four strike slip morphological indicators are observed at every site suggesting strike slip tectonism is indeed important to ganymede s evolutionary history byblus sulcus is the only mapped site where the presence of strike slip indicators is limited to only a few en echelon structures every other mapped site displays examples of at least two types with arbela sulcus containing candidate examples of all four in addition quantification of morphological characteristics suggests related rotation between sites as evidenced by the predominant nw se trend of mapped features within the light terrain present in five different sites nun tiamat uruk nippur philus byblus and anshar sulcus moreover incorporation of strike slip tectonism with pre existing observations of extensional behavior provides an improved synoptic representation of ganymede s tectonic history

formation of the double rift system in the thaumasia highlands mars 1 the thaumasia highland rifts are two complex graben structures in the thaumasia highland belt located in the southern thaumasia region mars the rifts are arranged 90 130 km apart in a nearly subparallel setting and represent a very unusual style of crustal deformation we have investigated the mechanism responsible for this peculiar style of rifting and found strain localization by volcanic weak zones to be a major factor for fault pattern formation indicating widespread prerift and synrift volcanic activity in the region this result is consistent with the high heat flow during rift emplacement as estimated from rift flank uplift our results indicate that the onset of volcanism predates the rift formation process and that magmatism and the associated lithospheric weak zones control the rift locations the simulations performed here are in good agreement with the observations for extension in the nw se to nnw sse direction and we favor a formation scenario involving passive rifting in a magmatectonically active environment

mind the gap an absence of valley fill deposits identifying the holocene hypsithermal period of enhanced flow regime in southeastern australia the holocene sedimentary record in southeastern australia is present in a range of landscape settings such as upland swamps dells internally drained lake basins alluvial fans and mid catchmen

uplift driven valley incision and river terrace formation in southern england outside the limits of middle pleistocene glaciation the river basins of southern england contain long cenozoic terrestrial sedimentary records of greatest importance are the river terrace sequences which contain biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary however trends in valley development cannot easily be accommodated within the framework of quaternary climatic change it is argued in this paper that episodic incision and terrace development result from uplift a consequence of the interplay between continuing alpine orogenic movements and erosion driven isostasy using a simple linear model height age an uplift rate of ca 7 cm ka 1 is estimated for the terrace sequence in the upper thames valley this preliminary model is evaluated using the records of adjacent basins 1997 john wiley sons ltd

tectonic history of the syria planum province of mars we attribute most of the development of extensive fractures in the tharsis region to discrete tectonic provinces within the region rather than to tharsis as a single entity one of these provinces is in syria planum faults and collapse structures in the syria planum tectonic province on mars are grouped into 13 sets based on relative age areal distribution and morphology according to superposition and fault crosscutting relations and crater counts we designate six distinct episodes of tectonic activity in the following chronologic order stage i is an early to late noachian deformation forming mostly east west structures fault set ia some large volcanoes also formed faults were produced possibly by flexural uplift also arcuate north trending grabens set ib indicate that faulting is transitional to the next stage stage ii is late noachian to early hesperian radial faulting centered in syria planum possibly due to isostatic uplift in late noachian set iia to early hesperian set iib time stage iii is early to late hesperian faulting tangential to syria planum that was related to local centers of uplift sets iii1 iii3 on the periphery of syria planum stage iv is a late hesperian graben formation that was circumferential to syria planum set iva caused either by collapse associated with eruption of magma or by flexure of the lithosphere due to volcanic loading in association with volcanism minor faulting occurred producing an oval pattern of faults in southwest syria planum set ivbl and a radial pattern south of the planum set ivb2 that apparently rejuvenated buried stage ii faults stage v is a late hesperian to early amazonian development of grabens and troughs of noctis labyrinthus and western valles marineris set v that was probably instigated by local uplift exposure of groundwater or ground ice zones may have produced further collapse and trough enlargement stage vi is early amazonian northwest trending faulting in noctis fossae set vil perhaps due to tharsis monies centered tectonism and north northwest normal faulting along the eastern side of the claritas rise set vi2 that was due to tectonic subsidence the duration of tectonic activity in the syria planum province was perhaps 2 3 b y photoclinometric topographic profiles across 132 grabens and fault scarps show that syria planum grabens have widths average of 2 5 km and most range from 1 to 6 km similar to lunar grabens but the martian grabens have slightly higher side walls average about 132 m and gentler wall slopes average of 9 and range of 2 25 than lunar grabens 93 m high and 18 slopes scarp degradation on mars has progressed through quakes impact shaking and dry slope processes the lower slopes may be due to mars higher gravity estimates of the amount of extension for individual grabens range from 20 to 350 m most estimates of the thickness of the faulted layer range from 0 5 to 4 5 km average is 1 5 km this thickness range corresponds closely to the 0 8 to 3 6 km range in depth for pits troughs and canyons in noctis labyrinthus and along the walls of valles marineris we propose that the predominant 1 to 1 5 km values obtained for both the thickness of the faulted layer and the depths of the pits troughs and theater heads of the canyons reflect the initial depth to the water table in this region as governed by the depth to the base of ground ice maximum depths for these features may indicate lowered groundwater table depths and the base of ejecta material

oblique rifting at tempe fossae mars this work shows the results of a structural study of the faults observed at the tempe rift northeastern tharsis region mars a new detailed map of faults and fault systems was used to geometrically characterize the fracture architecture of the tempe rift and to measure fault length displacement and spacing data to analyze the spatial distribution of fault centroids and to investigate the fractal nature of fault trace maps a comparison with analog models and the use of conventional techniques of fault population analysis show that the tempe rift was most probably generated under sinistral oblique rifting processes which highlights the importance of the presence of inherited fractures in the tectonic evolution of the noachian crust the angle between the extension direction and the rift axis varies along the tempe rift ranging from 50o 60o at its central southern part to 66o 88o to the southwest fault scaling relationships are similar to those found at midocean ridges on earth with exponential fault length frequency distributions localized inhomogeneous deformation generated weakly interacting faults spanning the entire thickness of the mechanical layer this thickness decreased from southwest to northeast along the rift along with distance from the central part of the tharsis dome

displacement length scaling for terrestrial and martian faults implications for valles marineris and shallow planetary grabens the displacement length ratio for the central composite graben in valles marineris inferred from topography and likely stratigraphic offsets to be d max l 4 6 x 10 3 is consistent with the scaling relations derived from terrestrial faults and grabens that also demonstrate a systematic variation in displacement with position along the structure the large 10 km depth in central valles marineris is therefore not unusual but rather should be expected for a fault system 2240 km long in contrast existing measurements of throw along the numerous shallow radial grabens in tharsis while apparently inconsistent with the scaling relations demonstrate the importance of recognizing mechanical segment length along linked or echelon graben sets faults on other planetary surfaces should scale with their terrestrial counterparts as long as they extend substantially deeper than the gravity dependent near surface rock mass zone 1 km for earth 2 5 km for mars

depositional environment and maturity of devonian pimenteira formation in the sao luis basin brazil abstract we carried out a detailed organic facies study on shale cutting samples from the devonian pimenteira formation in the sao luis basin northwest brazil to reconstruct the depositional paleoenvironment and origin of the organic matter samples were collected from the stratigraphic well 2 anp 5 ma and were analyzed for total organic carbon toc total sulfur s insoluble residue ri spore coloration index sci vitrinite reflectance ro palynofacies and biomarkers the toc values of the analyzed sediments range from 0 19 to 0 51 s from 0 17 to 0 85 and the total carbonate caco3 is low

fluviatile evidence for a period of late quaternary pluvial climate in coastal southeastern australia abstract the cranebrook terrace near sydney new south wales yields sound evidence of a period of exceptional fluvial activity in lowland basins of southeastern coastal australia well prior to the last glacial maximum this episode titled here the cranebrook pluvial is dated from radiocarbon and thermoluminescence age determinations as ending about 40 000 45 000 yr b p it was characterised along the lower nepean river by abundant gravel transported over a braid plain proximal to confining sandstone gorges thick basal gravels were deposited almost contemporaneously with a sandy clay overburden until this time when the river quite quickly became confined to two laterally stable channels additional overbank deposition probably accompanied this stable phase the easternmost channel was abandoned about 34 000 37 000 yr b p and the nepean river appears to have occupied only the western channel since then isolated from eustatic changes occurring downstream the nepean river has left no significant alluvial deposits from the last glacial maximum or from the holocene periods of time which in this fluvial environment appear quiescent by comparison with preglacial pluvial however stripping and replacement of the fine overburden appears to have occurred over the western part of the terrace about 14 000 yr b p or somewhat younger from 14 c determinations these conclusions are at odds with the proposal that the main period of alluvial deposition in coastal valleys of southeastern australia was triggered by widespread slope instability during the last glacial maximum alluvial and pollen data suggest the glacial was a cool dry period of relatively little fluvial activity in basins not affected by glaciation the cranebrook pluvial was probably the most important erosional depositional episode in the non glacially effected areas of southeastern australia in the last 50 000 years

topography of closed depressions scarps and grabens in the north tharsis region of mars implications for shallow crustal discontinuities and graben formation abstract using viking orbiter images detailed photoclinometric profiles were obtained across 10 irregular depressions 32 fretted fractures 49 troughs and pits 124 solitary scarps and 370 simple grabens in the north tharsis region of mars these data allow inferences to be made on the shallow crustal structure of this region the frequency modes of measured scarp heights correspond with previous general thickness estimates of the heavily cratered and ridged plains units the depths of the flat floored irregular depressions 55 175 m fretted fractures 85 890 m and troughs and pits 60 1620 m are also similar to scarp heights thicknesses of the geologic units in which these depressions occur which suggests that the depths of these flat floored features were controlled by erosional base levels created by lithologic contacts although the features have a similar age both their depths and their observed local structural control increase in the order listed above which suggests that the more advanced stages of associated fracturing facilitated the development of these depressions by increasing permeability if a ground ice zone is a factor in development of these features as has been suggested our observation that the depths of these features decrease with increasing latitude suggests that either the thickness of the ground ice zone does not increase poleward or the depths of the depressions were controlled by the top of the ground ice zone whose depth may decrease with latitude deeper discontinuities are inferred from fault intersection depths of 370 simple grabens assuming 60 dipping faults that initiate at a mechanical discontinuity in tempe terra and alba patera and from the depths of the large flat floored troughs in tempe terra the frequency distributions of these fault intersection and large trough depths show a concentration at 1 0 1 6 km depth similar to data obtained for syria sinai and lunae plana the consistency of these depth data over such a large region of western mars suggests that a discontinuity or a process that transcends local and regional geology is responsible for the formation of these features if this discontinuity is represented by the base of the cryosphere its uniform depth over 55 of latitude suggests that the cryosphere did not thicken poleward alternatively the concentration of depths at 1 0 1 6 km may represent the upper level of noneruptive dike ascent lateral dike propagation of mars which is controlled by gravity and atmospheric pressure and magma and country rock characteristics and was probably controlled in part by ground ice fault intersection depths in the north tharsis region locally extend down to a depth of 5 7 km the depth data between 2 and 3 km are attributed to the discontinuity at the interface of megaregolith and basement or to the upper limit of noneruptive dike ascent of magma with a high volatile content intersection depths greater than 3 km which were found at alba patera may be due to the megaregolith basement discontinuity which was buried and depressed by volcanic loading or to the upper level of noneruptive dike ascent of magma with a low volatile content the near absence of narrow simple grabens with fault initiation depths less than 0 6 1 0 km in this study area as well as in most of western mars suggests that this depth represents the minimum depth that normal faults can initiate at shallower depths tension cracks or joints would form instead this hypothesis is supported by the application of the griffith failure criterion to this minimum depth of normal fault initiation which suggests that shallow crustal materials have a tensile strength of 2 4 mpa throughout most of western mars in close agreement with previous estimates of tensile strength of martian basaltic rock

late cretaceous anoxic events in the brazilian continental margin abstract a combined geochemical and micropalaeontological study of cenomanian to maastrichtian pelitic sediments from the brazilian continental margin has been undertaken the organic carbon contents rock eval pyrolysis results and biological marker distributions together with the taxonomic selection and distribution patterns of microfossil assemblages indicate that intermittent anoxic events occurred in the brazilian marginal basins during the cenomanian santonian with deposition taking place in progressively deeper waters from neritic to bathyal such events are characterised by the following 1 i a predominance among the benthonic foraminifera of low diversity small sized specimens mainly composed of gavelinellids buliminids and nodosariids indicating dysaerobic bottom conditions 2 ii levels with virtually no benthonic foraminifera and a well developed planktonic biota foraminifera radiolarians and diatoms indicating anaerobic bottom conditions with oxygenated surface waters 3 iii the occurrence of organic rich calcareous mudstone sediments 4 iv features in the biological marker distributions such as high concentrations of 28 30 bisnorhopane and 25 28 30 trisnorhopane up to 130 ppm a predominance of phytane over pristane and medium to high concentrations of nickel and vanadyl porphyrins up to ca 5700 ppm the widely recognized cenomanian turonian and santonian oceanic anoxic events schlanger and jenkyns 1976 ryan and cita 1977 and jenkyns 1980 are therefore manifest in the cassipore ceara sergipe alagoas and campos basins within the brazilian continental margin as is the presence of such events in the coniacian in contrast the campanian maastrichtian appears to be a time interval when deposition under oxygenated conditions produced sediments with low organic carbon contents and poor hydrocarbon source potential containing highly diversified and abundant calcareous and agglutinated benthonic foraminifera

plinian eruptions and passive collapse events as mechanisms of formation for martian pit chain craters 1 three distinct and intersecting sets of graben exist near the martian volcano alba patera one set formed as a response to the evolution of the alba patera edifice a second set includes mainly linear structures widely interpreted to have formed in response to very large scale regional stresses the members of the third set contain numerous pit craters and we propose that these craters formed as a result of volcanic activity above long regional dikes emanating from a source to the south within the tharsis region the pit craters are of two morphologies small 2 km regular shaped ones usually completely contained within a graben but occasionally unbounded and larger 4 10 km irregular ones which commonly coalesce with one another we argue that these two types of crater formed by different but related mechanisms the smaller ones developed as the magma in a stalled dike degassed and volatiles were lost to the atmosphere via cracks and fractures in the overlying crustal rocks which then collapsed into the potential void space at the top of the dike producing the pit craters the larger craters formed subsequent to short lived explosive eruptions sourced from the underlying dike when the dike walls imploded and collapsed destroying evidence of any vent structures there are no visible products of these eruptions because the ambient martian atmospheric conditions caused the explosive eruptions to be very vigorous dispersing the products over very wide areas evidence indicates that both formation mechanisms occurred within very short distances over the same dike preexisting local tectonic stresses appear to have influenced the locations of the pit craters and groundwater may have been involved in determining their locations and the style of eruptive activity

reinterpretation of tractus fossae region as an asymmetric rift system on mars the tractus fossae region of mars is a wide area dominated by grabens normal faults and pit crater chains in this work based on previous studies on the area and the new interpretation of topographic data and morphological units based on images as a geologic framework we present a new insight on the origin of the graben structures as well as on the processes associated with the formation of the volcanic features here we propose a new model for this region on the basis of new measurements of graben extension and geological interpretations together with a reinterpretation of the stratigraphy and the geologic history of the area finally it is postulated that this region underwent a tectonic regime analog to an asymmetric rift system on earth

is the primordial crust of mars magnetized abstract a meteorite impact capable of creating a 200 km diameter crater can demagnetize the entire crust beneath and produce an appreciable magnetic anomaly at satellite altitudes of 400 km in case the pre existing crust is magnetized in this study we examine the magnetic field over all of the craters and impact related quasi circular depressions qcds with diameters larger than 200 km that are located on the highlands of mars excluding the tharsis bulge in order to estimate the mean magnetization of the highland crust using the surface topography and the gravity of mars we first identify those qcds that are likely produced by impacts the magnetic map of a given crater or impact related qcd is derived using the mars global surveyor high altitude nighttime radial magnetic data two extended ancient areas are identified on the highlands the south province and the tempe terra which have large number of craters and impact related qcds but none of them has an appreciable magnetic signature the primordial crust of these areas is not magnetized or is very weakly magnetized at most we examine some plausible scenarios to explain the weak magnetization of these areas and conclude that no strong dynamo existed in the first 100 myr of mars history when the newly formed primordial crust was cooling below the magnetic blocking temperatures of its minerals

late quaternary floodplain sedimentation along the pomme de terre river southern missouri abstract new cross sections and dates from along the pomme de terre river clarify the complex local history of valley development and floodplain sedimentation the observed history begins with a series of ancient bedrock strath terraces that record past bedrock valley positions at 15 5 to more than 58 m above the modern bedrock floor each strath is capped by 1 2 m of channel gravel and sand permeated by red clay sometime previous to ca 140 000 yr b p a much lower bedrock valley only about 5 6 m above the modern level was excavated by 140 000 yr b p accumulation of red and gray mottled silty clay had commenced and had reached to 8 5 m above the modern floodplain before 48 900 900 14 c yr b p sometime between ca 49 000 and 45 000 14 c yr b p erosion caused abandonment of an oxbow meander and lowered the bedrock valley to about its present depth younger yellowish red and gray mottled silty clay alluvium then began accumulating this mid wisconsinan fill reached to 2 5 m above the modern floodplain sometime before 31 800 1340 14 c yr b p at which time another erosional phase was in progress a late wisconsinan olive clay accumulated between 27 480 1950 and ca 23 000 14 c yr b p followed by approximate stability until 13 550 400 14 c yr b p after stability an erosional episode began but by 10 200 330 14 c yr b p deposition of a distinctive brown clayey silt was underway this early holocene fill reached to about the same level as the mid wisconsinan fill by 8100 140 14 c yr b p erosion occurred between this date and 7490 170 14 c yr b p but the former floodplain level was rapidly reattained and was apparently stable until ca 5000 14 c yr b p finally erosional unconformities and 17 dates from the brown clayey silt and from younger grayish brown silty sand underlying the modern floodplain record subsequent episodes of floodplain erosion at ca 5000 2900 1500 and 350 14 c yr b p the timing of pomme de terre floodplain sedimentary regimes characterized by net aggradation erosion or stability may have been controlled by climate in particular both periods of stability appear to have been coeval to times of strongly zonal upper atmospheric circulation intensified zonal circulation would have resulted in less frequent large floods and an increased dominance by floods of small to moderate size in contrast there are no obvious parallels to be drawn between this local alluvial history and sea level or glacial outwash induced baselevel changes

a 40 000 year vegetation history and climatic interpretations of burraga swamp barrington tops new south wales abstract burraga swamp a small basin surrounded by cool temperate rainforest at 985 m in the central new south wales highlands has provided a record of 40 000 years from 40 000 30 000 years bp the site was a lake with a very slow rate of deposition of fine grained sediments and flourishing aquatic swamp vegetation the dryland vegetation was an open or sparsely treed grassland herbfield from 30 000 21 000 years bp the dryland vegetation remained much the same but the aquatic vegetation disappeared from 21 000 17 500 years bp sandy sediments were deposited at an accelerated rate culminating in a layer of gravelly sand possibly the result of periglacial activity only one band of clay in this section contained sufficient pollen to study indicating treeless vegetation after 17 000 years bp the rate of sediment accumulation slowed or ceased and after 15 000 years some mesic elements started to return at 6500 years bp peat started forming and cool temperate rainforest was fully developed remaining on the site to the present this site extends the record of treeless condition at the last glacial maximum to more northerly localities than previously known