a continental scale mosaic of the amazon basin using jers 1 sar a methodology example and accuracy assessment are given for a continental scale mosaic of the amazon river basin at 100 m resolution using the jers 1 satellite this unprecedented resource of l band sar data collected by jers 1 during the low flood season of the river amounts to a collection of 57 orbits of the satellite and a total of some 1500 1 k spl times 1 kb images interscene overlap both in the along track and cross track directions allows common reference points to be used to correct individual scene geolocation inaccuracies that have been derived from the satellite ephemeris the set of common reference points is assembled into a matrix formulation that is used to solve for individual scene geometric offsets by correcting for these offsets each scene is placed within a global coordinate system which can then be used as the basis for creating a final visually seamless mosaic the methodology employed in this approach allows for a mathematical foundation to be applied to the mosaicking process as well as providing a unique traceable solution for correctly geolocating satellite imagery

climatic control on the late permian main dolomite ca2 deposition in northern margin of the southern permian basin and implications to its internal cyclicity

topography and tectonics of the central new madrid seismic zone results of numerical experiments using a three dimensional boundary element program we present results of a series of numerical experiments designed to test hypothetical mechanisms that drive deformation in the new madrid seismic zone experiments are constrained by subtle topography and the distribution of seismicity in the region we use a new boundary element algorithm that permits calculation of the three dimensional deformation field surface displacement fields are calculated for the new madrid zone under both far field plate tectonic scale and locally derived driving strains results demonstrate that surface displacement fields cannot distinguish between either a far field simple or pure shear strain field or one that involves a deep shear zone beneath the upper crustal faults thus neither geomorphic nor geodetic studies alone are expected to reveal the ultimate driving mechanism behind the present day deformation we have also tested hypotheses about strain accommodation within the new madrid contractional step over by including linking faults two southwest dipping and one vertical recently inferred from microearthquake data only those models with step over faults are able to predict the observed topography surface displacement fields for long term relaxed deformation predict the distribution of uplift and subsidence in the contractional step over remarkably well generation of these displacement fields appear to require slip on both the two northeast trending vertical faults and the two dipping faults in the step over region with very minor displacements occurring during the interseismic period when the northeast trending vertical faults are locked these models suggest that the gently dipping central step over fault is a reverse fault and that the steeper fault extending to the southeast of the step over acts as a normal fault over the long term

calcretes at sequence boundaries in upper carboniferous cyclothems of the sydney basin atlantic canada abstract nodular and associated groundwater calcretes in coal bearing cyclothems of the sydney basin mark the boundary between underlying marginal marine and overlying alluvial deposits they are inferred to represent lowstand surfaces sequence boundaries the host sediments include both sand siltstones and palustrine limestones microfabrics of calcretes with detrital hosts show evidence of replacement displacement and shrinkage alpha fabrics suggesting that the calcretes formed under relatively arid conditions in contrast microfabrics of nodular calcretes with limestone hosts exhibit predominantly beta fabrics with root induced brecciation and subordinate shrinkage fabrics the calcretes and host limestones are inferred to have formed in topographic lows thick alluvial sediments with red calcic vertisols overlie the calcretes and formed within the transgressive systems tract under conditions of abundant sediment supply coals and associated hydromorphic palaeosols lie near the transgressive maximum and in the highstand systems tract the presence of calcareous palaeosols on lowstand surfaces suggests that the lowstands were times of relative climatic aridity

holocene climate history of coastal southwestern australia using calcrete as an indicator sheets of groundwater calcrete in the stratigraphic sequences of beach dune units deposited in the interval mid holocene present record a history of variable holocene climate studies of holocene coastal plain areas of the perth basin spanning a gradient of climate from humid to semi arid show that calcrete today is clearly forming as a sheet just above the water table in the zone of capillary rise in humid environments as thin isolated lenses under distinct outliers of vegetation zones in subhumid environments and not at all in semi arid zones however such calcrete sheets are not widespread earlier in the holocene at levels where former water table positions can be inferred at the various localities evidently apart from small isolated lenses calcrete sheets did not develop at most localities earlier in the holocene the very distinct sealevel history and the corollary a distinct water table history of holocene coastal plain sequences enable a reconstruction of calcrete history because each water table level should have a distinct calcrete sheet if it was developed the evidence shows a mid to late holocene period of relatively more arid conditions and an extension of more humid climates only in the past 2800 14c yrs

changing fluvial environments across the permian triassic boundary in the karoo basin south africa and possible causes of tetrapod extinctions abstract the karoo supergroup is a 12 km thick succession of sedimentary rocks that accumulated in a large intracratonic retroarc foreland basin in southwestern gondwana the strata record 100 million years of almost continuous sediment accumulation from the permo carboniferous 300 ma through to the early jurassic 190 ma under a range of climatic regimes and within several tectonically controlled sub basins alluvial sediments dominate the succession from the late permian onwards fossils of synapsid reptiles and early dinosaurs are sufficiently common to be used in a ten fold biostratigraphic subdivision of these strata the permian triassic boundary in the karoo succession is marked by a major extinction of the herbivorous dicynodonts which co incides with a rapid change in fluvial facies this study uses field observations of the sedimentary facies palaeosols and in situ fossils of well exposed p tr boundary sequences in the southern karoo basin to provide evidence of environmental changes that may have caused the tetrapod extinctions in the main karoo basin below the p tr boundary sequence the sediments comprise drab greenish grey mudrocks with a few thick 3 12 m multistoried laterally accreted fine grained sandstone bodies the mudrocks host hydromorphic palaeosols with palustrine carbonate horizons and mostly disarticulated skeletal remains of dicynodon assemblage zone fauna above a transition zone of approximately 20 m thickness these strata change into reddish brown mudrocks with numerous thin 0 5 5 m ribbon sandstone bodies and more continuous sheet sandstones calcic palaeosols with rhizocretions nodular horizons and pervasive calcareous encrustation of articulated skeletons of lystrosaurus and associated fauna of the lystrosaurus assemblage zone within a 20 m thick interval of the transitional strata fossils of dicynodon and lystrosaurus occur together the facies transition that co incides with the latest permian dicynodont extinction is interpreted as a change in fluvial style from meandering to low sinuosity channels with general drying of the floodplain habitats and redistribution of vegetation belts the horsetails in particular became significantly reduced in areal distribution the changes in fluvial style in the karoo basin at the end of the permian were triggered by a pulse of thrusting in the southerly source area dated at 247 ma 2 ma which brought about rapid progradation of a large sandy braided fan system the katberg sandstone fm into the central parts of the basin a concomitant basinward migration of depositional environments allowed the lystrosaurus communities that were adapted to dry floodplains to colonise the entire basin to the detriment of most of the wet floodplain dicynodon fauna that lived there

climatic records over the past 30 ka from temperate australia a synthesis from the oz intimate workgroup temperate australia sits between the heat engine of the tropics and the cold southern ocean encompassing a range of rainfall regimes and falling under the influence of different climatic drivers despite this heterogeneity broad scale trends in climatic and environmental change are evident over the past 30 ka during the early glacial period 30 22 ka and the last glacial maximum 22 18 ka climate was relatively cool across the entire temperate zone and there was an expansion of grasslands and increased fluvial activity in regionally important murray darling basin the temperate region at this time appears to be dominated by expanded sea ice in the southern ocean forcing a northerly shift in the position of the oceanic fronts and a concomitant influx of cold water along the southeast including tasmania and southwest australian coasts the deglacial period 18 12 ka was characterised by glacial recession and eventual disappearance resulting from an increase in temperature deduced from terrestrial records while there is some evidence for climatic reversals e g the antarctic cold reversal in high resolution marine sediment cores through this period the high spatial density of holocene terrestrial records reveals an overall expansion of sclerophyll woodland and rainforest taxa across the temperate region after 12 ka presumably in response to increasing temperature while hydrological records reveal spatially heterogeneous hydro climatic trends patterns after 6 ka suggest higher frequency climatic variability that possibly reflects the onset of large scale climate variability caused by the el nino southern oscillation

paleoclimatic signature in terrestrial flood deposits large scale process simulation was used to reconstruct the geologic evolution during the past 600 000 years of an alluvial fan in northern california in order to reproduce the sedimentary record the simulation accounted for the dynamics of river flooding sedimentation subsidence land movement that resulted from faulting and sea level changes paleoclimatic trends induced fluctuations in stream flows and dominated the development of the sedimentary deposits the process simulation approach serves as a quantitative means to explore the genesis of sedimentary architecture and its link to past climatic conditions and fault motion

fitting degradation of shoreline scarps by a nonlinear diffusion model the diffusion model of degradation of topographic features is a promising means by which vertical offsets on holocene faults might be dated in order to calibrate the method we have examined present day profiles of wave cut shoreline scarps of late pleistocene lakes bonneville and lahontan it may be assumed that these scarps were initially at least as steep as the angle of repose offsets range from 1 to 12 m and present slope angles range from 9 to 29 a parameter called apparent diffusion age defined as half the mean square horizontal extent of the slope function of each profile is plotted as a function of scarp offset the points show a clear trend of apparent age increasing nearly linearly with offset if linear diffusion held and scarps were initially vertical apparent diffusion age would be the same for all the shoreline profiles the increasing trend can only partly be explained by nonvertical initial scarp slope and therefore the rate of transport of material downslope must increase significantly faster than a linear law in the range of slopes spanned by the data the transport law must become linear at small slope to reduce scatter between profiles with varying ambient slopes the transport law adopted for the purpose of dating is k0 1 5s2 where s is local slope the transport coefficient k0 is correlated inversely with fan slope suggesting that there is a dependence on the particle size distribution a table is included that allows easy application of the model to scarps with simple initial shape

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

the permian moradi formation of northern niger paleosol morphology petrography and mineralogy abstract three basic paleosol morphologies named type a type b and type c are described from the middle upper permian strata of the moradi formation tim mersoi basin northern niger the moradi formation is a typical alluvial redbed succession dominated by red mudrocks with fine to coarse grained pebbly channel sandstones and matrix breccias type a paleosols are hosted by well sorted fine to medium grained trough cross bedded and massive sandstones and preserve abundant vertical to horizontal micritic and microspar calcite tubules interpreted as rhizoliths lateral variability of rhizoliths in type a paleosols and their close association with fluvial channel fill sediments suggests they are the roots of grove stands of phreatophytic vegetation that grew within unstable anabranching stream systems type b paleosols are hosted by mudrocks and preserve well developed ped structure abundant micritic calcite nodules and vertically stacked micritic calcite nodular bodies as well as rare calcite with satin spar texture interpreted as a pseudomorphic replacement of pedogenic gypsum the morphology of type b paleosols suggests they were formed in well drained floodplain deposits on stable landforms type c paleosols are similar to type b but preserve pedogenic structures indicative of soil volume expansion and contraction as well as more abundant stage ii pedogenic carbonate nodules the morphology of type c paleosols suggests that they developed periodically rather than seasonally in poorly drained deposits that nevertheless occupied a relatively stable part of the landscape such as the plains flanking ephemeral lakes or sabkhas x ray diffraction analysis of the the range of morphologies petrographic textures and mineralogy of the paleosol profiles indicates semi arid to hyper arid climatic setting this paleoclimatic reconstruction is in agreement with middle and late permian conceptual paleoclimate models and quantitative general circulation models nevertheless and in spite of an arid climate moradi paleosols and their host strata also indicate a relatively shallow groundwater table importantly this shallow groundwater resource undoubtedly helped to support the moderately diverse fossil vertebrate assemblage and large stature macrophytes preserved in the moradi formation

fluvial landsculpting and the fractal dimension of topography abstract quantitative models of landform development can help us to understand the evolution of mountains and regional topography and the effects of tectonic motions and climate on landscape including its fractal geometry this paper presents a general and powerful three dimensional model of fluvial erosion and deposition at hill to mountain range scale the model works by accumulating the effects of randomly seeded storms or floods precipitons that cause diffusional smoothing then move downslope on digital topography grids that erode portions of elevation differences that transport a slope limited amount of eroded material and that deposit alluvium when their sediment carrying capacity is exceeded the iteration of these simple and almost linear rules produce very complicated simulated landscapes demonstrating that complex landscapes do not require complex laws each process implemented in the model is affected differently by changes in horizontal scale erosion a scale free process roughens topography at all wavelengths this roughening is balanced by diffusive processes scaling as 1 l 2 at short wavelengths and deposition scaling scaling as 1 l 2 at long wavelenghts such a mixture of scale free and scale dependent processes can produce multifractal behavior in the models the fractal dimension of the model topography is much more sensitive to climatic variables than to tectonic uplift landscape evolution may be fractal but it does not seem to be chaotic analysis of topography of areas in southern arizona using variograms shows approximately fractal behavior with mean fractal dimension around 2 2 2 3 departures from an exact fractal relatioship imply that the topography is in detail multifractal the fractal dimension at short wavelengths is less than that at long wavelengths this variation could either be caused by the relative strengths of diffusive and erosional processes shaping the topography or a result of changes in climatic or tectonic conditions still preserved in the landscape

on the occurrence of caliche pisolites from the western continental shelf of india abstract pisolitic limestones collected from the western continental shelf of india at a depth of 60 m showed characters similar to caliche pisolites low magnesium calcite and quartz are the major minerals in the pisolites polished sections show downward thickening of pisolites with intermittent macro and microfractures micrite showing clotted and pelloidal texture is the dominant component of the pisolites they further consist of calcite crystal structures resembling microcodium root voids filled with sparry calcite and reddish brown peloids spherulitic structures exibiting radial patterns of calcite formed by the neomorphism of microcodium have been identified fibrous calcite cement occurs as replacement after prismatic calcite and as terminal expansion of prism faces acicular calcites flower spar calcites and dendritic calcites which owe their origin due to intense evaporation are also found the environmental conditions for the formation of caliche pisolites are discussed it is suggested that these caliche pisolites represent continental conditions of the shelf during the holocene and are formed by pedogenic soil processes in association with a semi arid climate and moderate rainfall

a calcrete based u th chronology for landform evolution in the sorbas basin southeast spain nodular and massive calcretes from alluvial terraces in the sorbas area of southeast spain have been dated by the u th isochron method to between 8 350 ka alternative approaches have been used to generate the multiple samples for the isochron method for several of the calcretes dates agreed closely when obtained by total dissolution of a number of nodules or by the sequential dissolution in different acids of a single nodule however fractional dissolution of a single nodule in the same acid revealed two stages of precipitation of different age it is considered that the calcretes may not be strictly pedogenic in origin and that groundwater processes linked to the alluvial environment may have been involved also nevertheless their dates provide minimum ages for a chronostratigraphic framework for terrace evolution

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

climate fluctuations recorded in phreatic and vadose calcretes of the lower carboniferous clyde sandstone formation of machrihanish kintyre peninsula sw scotland the galdrings cliffs of machrihanish in the kintyre peninsula of scotland expose a lower carboniferous clastic succession that hosts a wide variety of calcretes including thick and massive host replacing phreatic calcrete hardpans hrpchs which are geologically rare and which are the products of a thorough replacement of host minerals by calcite in the mixing zone between fresh and evaporitic groundwaters isotopic values of 53 samples from various calcretes distributed in a c 45 m thick succession provided well defined trends of covariance between carbon and oxygen isotopes thus delineating trends of aridification and humidification from the interplay of precipitation and evaporation rates although values from hrpchs are more constrained all other forms of calcrete in the succession pedogenic nodules pillar calcrete laminar calcrete and invasive phreatic calcrete cement in sandstone follow similar stable isotopic trends an aridification trend preceded the formation of each hrpch occurrence corroborating studies on modern equivalents that suggest that they develop in the more arid range of calcrete formation the better constrained isotopic values of hrpchs compared with those of more common forms of calcrete are interpreted to be indicative of more specific environmental requirements which may in part explain their rarity in the geological record

the generation of sar layover and shadow maps from digital elevation models as almost fully automated techniques as well as expert systems obtain more and more importance in the geocoding of synthetic aperture radar sar images the solution to the problem of the identification of homologue points between the sar image and reference system moves into the fields of pattern recognition and feature matching shadow regions which appear as dark regions in the sar image are independent from the backscattering of the imaged terrain due to the multiplicity of signals layover regions appear brighter than the surrounding regions hence the phenomena of layover and shadow are stressed in the present paper the reasons for their occurrence are studied through the digital elevation model representing the earth s surface an algorithm to define layover and shadow regions directly in the geometry of the digital elevation model is presented the results are given in a so called layover and shadow map

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

the global rain forest mapping project jers 1 radar mosaic of tropical africa development and product characterization aspects the global rain forest mapping project grfm is an international collaborative effort initiated and managed by the national space development agency of japan nasda the main goal of the project is to produce a high resolution wall to wall map of the entire tropical rain forest domain in four continents using the l band sar onboard the jers 1 spacecraft the processing phase which entails the generation of wide area radar mosaics from the raw sar data was split according to the geographic area in this paper the focus is on the part related to africa the grfm project s goal calls for the coverage of a continental scale area of several million km sup 2 using a sensor with the resolution of tens of meters in the case of the african continent this entails the assemblage of some 3900 high resolution sar scenes into a bitemporal mosaic at 100 m pixel spacing and with known geometric accuracy while this fact opens up an entire new perspective for vegetation mapping in the tropics it presents a number of technical challenge the authors report on the solutions adopted in the grfm africa mosaic development and discuss some quantitative and qualitative aspects related to the characterization and validation of the grfm products in particular the mosaic geolocation and its validation are discussed in detail indeed the internal geometric consistency subpixel accuracy in the coregistration of the two dates and the absolute geolocation residual mean squared error of 240 m with respect to ground control points are key features of the grfm africa mosaic

recognition of supraglacial debris in the tianshan mountains on polarimetric sar images abstract debris cover is widely present in the ablation areas of mountain glaciers such debris plays an important role in glacier mass balance but it complicates the glacier boundary and area estimation when using remotely sensed images automatic recognition of the debris is much more difficult than recognizing bare ice on optical remotely sensed images because the debris has almost the same spectral characteristics of the surrounding terrain in this paper the scattering characteristics of the debris on the c and l band polarimetric sar images are presented and analyzed to study the possibility of recognizing debris thickness and extent the koxkar glacier in the central tianshan mountain range was selected as the study area it was found that debris is distinct from bare ice in cross polarization hv of both the l and c bands the l band volume scattering component acquired from target decomposition increases with debris thickness when the debris is less than 25 cm deep but the volume scattering does not increases if the debris is thicker than 25 cm in contrast the c band sar data does not appear to be sensitive to debris thickness this difference may be caused by different radar penetration depth of the debris on the basis of the polarimetric property analysis two methods were developed to determine the extent of the debris in the first method the simple threshold to distinguish debris from non debris areas is presented using this threshold approximately 90 of the debris can be recognized in the second method by combining more polarimetric features and support vector machines recognition of debris reaches an accuracy greater than 95

calcrete breccia floatstone in holocene sand developed by storm uprooted trees abstract calcrete breccia floatstone occurs as a surficial sheet overlying calcrete caliche in southwestern australia the sheet is composed of calcrete clasts of variable size dispersed within a sand or soil matrix the calcrete breccia floatstone is developed as trees are uprooted and toppled by periodic severe storms these trees disrupt a portion of the underlying calcrete in which their roots are imbedded and subsequent decay or burning releases calcrete clasts to the surficial sand environment this process provides an additional mechanism for producing calcrete breccia the configuration of calcrete sheet and overlying breccia floatstone also provides useful information for interpretation of palaeo environmental conditions and processes

complex fault interactions in a restraining bend on the san andreas fault southern santa cruz mountains california the unusual oblique thrust mechanism of the october 18 1989 loma prieta earthquake focused attention on the complex tectonic setting of this segment of the san andreas fault near the mainshock epicenter the san andreas fault curves to the left defining a restraining bend the large thrust component of the mainshock focal mechanism is consistent with the horizontal compression expected across restraining bends however repeated loma prieta type earthquakes cannot exclusively produce the observed topography of the southern santa cruz mountains the highest point of which experienced subsidence during the 1989 earthquake in this paper the authors integrate seismic geomorphic and tectonic data to investigate the possibility that motions on faults adjacent to the san andreas fault play an important role in producing the observed topography the three dimensional geometry of active faults in this region is imaged using the loma prieta preshock and aftershock sequences the most conspicuous features of the fault geometries at depth are 1 the presence of two distinct zones of seismicity corresponding to the san andreas and the sargent berrocal fault zones 2 the concave upward shape of the loma prieta rupture surface 3 the reduction in dip of the deepest portions of the rupture plane asmore the mainshock hypocenter is approached 4 the apparent transfer of shallow slip in some areas from faults in the san andreas fault zone to those in the sargent berrocal fault zone and 5 the presence of a deep northeasterly dipping plane associated with the sargent berrocal fault zone the authors find that a model of fault interactions which involves displacement on faults in both the san andreas and the sargent berrocal fault zones is consistent with loma prieta coseismic displacements preshock and aftershock seismicity and observed topography less

monitoring glacier zones and snow firn line changes in the qinghai tibetan plateau using c band sar imagery abstract small glaciers and ice caps in mountainous areas are often sensitive indicators of local and global climate change in this paper typical continental glaciers the dongkemadi and its neighbouring glaciers in the central area of the qinghai tibetan plateau are monitored using multi sensor c band synthetic aperture radar sar imagery the study includes analysis of the alternating processes of ablation and freezing the glacier zones detected on sar images and the changing snow firn line across different days seasons and years experiments show that in late summer the wet snow firn ice boundary which is termed the late summer wet snow firn line wsfl is easily detected on sar images and it is relatively stable over multiple days also the detected late summer wsfl and the recorded yearly equilibrium line which reflects glacier mass balance are close in a positive mass balance year but the detected late summer wsfl is lower than the equilibrium line in a negative mass balance year by combining pit and sar observations it was found that the firn can be divided into two parts on the glaciers the thick firn that lies in the neve basin is distinct on sar images in winter but the firn surrounding the basin with thickness ranging from 0 to 20 cm is difficult to recognize the thick firn line the lower boundary of neve basin is stable in observations eight years apart based on the c band vv polarization sar image experiments field work and existing records the spatiotemporal backscatter signature specific to the typical continental glacier is identified the spatiotemporal backscatter signature helps to understand mass balance proxies and surface melt patterns of the glaciers in sar images

evolution of the northern santa cruz mountains by advection of crust past a san andreas fault bend the late quaternary marine terraces near santa cruz california reflect uplift associated with the nearby restraining bend on the san andreas fault excellent correspondence of the coseismic vertical displacement field caused by the 17 october 1989 magnitude 7 1 loma prieta earthquake and the present elevations of these terraces allows calculation of maximum long term uplift rates 1 to 2 kilometers west of the san andreas fault of 0 8 millimeters per year over several million years this uplift in concert with the right lateral translation of the resulting topography and with continual attack by geomorphic processes can account for the general topography of the northern santa cruz mountains

dedolomitization of dolocrete deposits in kuwait arabian gulf dedolomitization of a dolocrete profile hosted in mio pleistocene siliciclastic deposits in the area of kuwait city arabian gulf was investigated dolocrete dolomite crystals vary considerably in size shape and internal structure however they are mostly zoned zonation is usually due to the alteration of cloudy and clear zones the cloudy zones which are mostly formed of disordered metastable dolomite are more susceptible to dedolomitization than the stable well ordered clear zones two modes of dedolomitization were recognized the first involves complete dissolution of the metastable dolomite followed by precipitation of intracrystalline cavity filling calcite the second is a pseudomorphic replacement of dolomite by calcite this replacement takes place by the simultaneous dissolution of dolomite and precipitation of calcite in such a manner that the original dolomite fabrics are inherited in the dedolomite exposed and near surface dolocrete profile less than 5 m deep are almost completely dedolomitized and altered to secondary calcrete whereas subsurface profiles are slightly dedolomitized dedolomitization of the sub surface dolocrete profiles may indicate the effect of flushing by fresh groundwater which flows from west to east whereas the alteration of the exposed dolocrete profile could be attributed to be an effect of meteoric water a new mode of calcrete genesis by dedolomitization and or complete calcitization of precursor dolocrete is suggested

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

occurrence of phreatic dolocrete within tertiary clastic deposits of kuwait arabian gulf abstract the term dolocrete is used in the present study to describe siliciclastic sediments which are partially or completely cemented and or replaced by terrestrial phreatic dolomite several successive dolocrete profiles occur within the subsurface tertiary fluviatile muddy sand and mudstone deposits in kuwait city three zones were recognized within these dolocrete profiles these are in descending order 1 dolocrete band 2 dolocrete nodules and 3 incipient dolocrete dolocrete also occurs within the compact green mudstone layers the studied dolocrete comprises detrital grains inherited from the host sediment and authigenic minerals precipitated during the dolocretization processes the detrital grains include mainly quartz feldspars illite and smectite the abundance of authigenic minerals dolomite calcite and palygorskite relative to detrital grains reflects the degree of dolocrete maturation mature dolocrete is chiefly composed of dolomite and palygorskite several dolomite fabrics and textures were recognized however dolocretic dolomite is generally present as incomplete rhombohedra with spiky terminations variation in the nature of host sediment and diagenetic conditions are responsible for the degree of dolocretization and diversity of fabrics and textures it is suggested that the dolocrete was developed by the precipitation of dolomite from pore solution saturated with respect to dolomite within the phreatic zone three main sources of chemicals required for dolocretization are suggested 1 mg rich groundwater from the dolomitic dammam formation 2 mg and co 2 released from clay minerals and organic matter in the host sediment mud matrix and 3 infiltrated meteoric water

correlation between the geologic record and computed plate motions for central california we have attempted to correlate geologic events in part of central california with computed motions of oceanic plates relative to cratonic north america three composite terranes are considered 1 the sierra nevada 2 the coast ranges northeast of the san andreas fault and 3 the salinian block in the sierra nevada jurassic plutonism ending about 147 m y b p and cretaceous plutonism 120 80 m y b p correlate with deduced farallon north america fa na convergence as does the nevadan orogeny 158 153 m y b p however the gap in plutonism 146 121 m y b p outlasted by far an apparent minimum in convergence 145 135 m y b p magmatism ceased in the sierra and uplift slowed during the laramide orogeny 75 45 m y b p when tectonic activity had moved east to the site of the rockies presumably because of a low angle of subduction but volcanisin resumed in the sierra about 33 m y b p indicating that a steeper angle was reestablished apparently east west compression slackened when the pacific north america pa na transform regime developed basalt was erupted in the southern sierra 12 3 m y b p and during this same time the range started its most rapid rise as a normal fault bounded block the coast ranges north east of the san andreas fault are underlain by the franciscan complex the older parts of the complex were probably assembled in a subduction zone far south of their present location but we believe that the same fa na convergence that was cited for sierran plutonism was responsible despite the disparity in latitude as the farallon plate was probably in contact with most of the western margin of north and south america a perceived strong pulse in convergence 100 85 m y b p evidently produced the coast range thrust which on geologic grounds alone most likely originated between 96 and 88 m y b p some of the northwesterly transport of franciscan rocks relative to north america is ascribed to oblique kula north america ku na convergence 85 43 m y b p during which period the coast range thrust was revived about 60 m y b p the farallon plate again influenced the california margin after the kuia plate had moved northward and fa na convergence caused the accretion of the coastal belt and king range terranes of the neo franciscan the advent of pacific north america pa na interaction was marked by local volcanism which advanced from the southeast toward the northwest in consonance with the passage of the mendocino triple junction dickinson and snyder 1978 in the salinian block plutons 107 82 m y old can be ascribed to the same fa na convergence as the contemporary cretaceous plutons of the sierra nevada although the salinian intrusives originated much farther south paleomagnetic results champion et al 1980 from the salinian related pigeon point formation 75 71 m y in age suggest about 2500 km of poleward essentially coastwise movement this postulated large movement during part or all of the last 75 m y poses the greatest dilemma in our study the kuia is the only known plate whose computed obliquely convergent motion is appropriate for the late cretaceous paleogene part of the migration and even this motion is inadequate for the estimated transport within the most likely time window furthermore the farallon plate seems ideally suited for the laramide orogeny 70 45 m y b p both plates could not have been in contact with the same part of the margin at the same time oblique convergence of the kula plate could possibly have caused large coastwise transport and also the laramide orogeny the coast ranges northeast of the san andreas fault and the salinian block both experienced strike slip faulting and en echelon folding correlative with pa na interaction indicating that they were close together by neogene time faulting and folding have been particularly marked since the inception of spreading in the gulf of california and attachment of westernmost california to the pacific plate about 4 m y b p the rise of individual coastal ranges commencing 3 1 m y b p may possibly have been caused by slight convergence which appears in computed pa na relative motions from 5 m y b p to the present

pedogenic carbonates on precambrian silicate rocks in south india origin and paleoclimatic significance abstract calcrete in alfisols on precambrian silicate rocks is studied here in an attempt to reconstruct paleorainfall trends in semiarid south india facies of observed carbonate accumulation are pseudomycelium calcrete nodules nodular horizons hardpan and laminar horizons based on geochemical and sr isotope tracing we relate the presence of calcrete to local geologic conditions within the precambrian basement notably discrete ca rich metamorphic outcrops and rule out eolian input micromorphologic analysis reveals a multi stage origin of the calcretes involving soil colluvial geochemical and biologic processes mostly in vadose environments preliminary u th ages of 190 200 ka obtained on calcrete nodules suggest a major phase of ca release rock weathering and precipitation during marine oxygen isotope stage 7 the calcrete thus indicates fairly stable semiarid conditions at the 200 ky time scale despite fluctuations around an annual rainfall average close to current values 700 mm the stability of the western ghats barrier as a shield to the southwest monsoon explains the long term average stability of the pedoclimatic environment in the rainshadow zone the radiometric ages suggest that weathering may occur massively at discrete intervals of geologic history during spikes of humidity in the paleoclimatic record the rest of the time is spent recycling and redistributing the products of weathering incrementally at landscape scale within seasonal cycles of a relatively stable semi arid climate dating the calcrete therefore does not equate with dating the soil but instead the residence times of nodules in a dynamic soil system in which different constituents have different turnover rates

the distribution and discrimination of shallow authigenic carbonate in the pliocene pleistocene palomas basin southern rio grande rift nine types of authigenic carbonate are present in the pliocene pleistocene alluvial fan and axial fluvial sediment of the palomas half graben in the southern rio grande rift pedogenic and other vadose carbonate includes 1 pedogenic carbonate of stage ii and stage iii morphology underlying bw and bt horizons 2 mudstones in which the carbonate nodules may be pedogenic or the result of shallow groundwater invasion of the vadose zone 3 pedogenic calcic nodules and tubules in eolian sand and 4 gully bed cement of proximal fan conglomerates formed by infiltration and evaporation of surface runoff shallow groundwater carbonate exists as 5 thin 30 50 cm massive beds with an upper fringe of nodules and tubules precipitated at the water table and in the capillary fringe 6 thick 1 5 3 m massive beds deposited by lateral flow of groundwater or at springs and 7 thin 30 cm calcified root mats associated with near surface water saturated sediment or springs phreatic spar cements 8 occupy the interstices of conglomerates and sandstones and locally exist as 9 oriented concretions groundwater carbonates are best developed near the toes of the large hanging wall derived alluvial fans whereas phreatic cement preferentially exists in footwall derived alluvial fan conglomerates pedogenic carbonate is distinguished from groundwater carbonate by the association with other diagnostic paleosol horizons a predominantly vertical arrangement of root traces peds desiccation cracks and calcic tubules and by gradational contacts the 13 c and 18 o values are similar among pedogenic and shallow groundwater carbonate although locally nodules in eolian sand and gully bed cement have higher 18 o values perhaps due to the effects of evaporation some phreatic cements may be distinguished from pedogenic and shallow groundwater carbonate by lower values of 13 c and 18 o authigenic carbonate in footwall derived alluvial fan sediment has consistently higher values of 13 c than that in hanging wall derived sediment which may reflect differences in vegetative type and or density on either side of the basin

geodetic estimate of coseismic slip during the 1989 loma prieta california earthquake offsets in the relative positions of geodetic stations resulting from the loma prieta earthquake can be explained with a dislocation model that includes buried oblique slip on a rupture surface extending 37 km along the strike of the san andreas fault dipping 70 degree to the sw and extending from a depth of about 5 to 17 5 km assuming uniform slip on a rectangular surface the mean values for a range of reasonable fault geometries are 1 6 plus minus 0 3 m right lateral strike slip and 1 2 plus minus 0 3 m reverse slip slip on an adjacent extension of the rupture to the southeast recorded in the aftershock sequence is not well constrained by the geodetic data the geodetic data clearly preclude rupture extending near the surface

calcic vertisols in the upper daptocephalus assemblage zone balfour formation karoo basin south africa implications for late permian climate

evolution of the santa cruz mountains california through tectonic growth and geomorphic decay i describe a strategy for modeling a specific large scale topographic feature that recognizes the discrepancy between tectonic and geomorphic scales and allows for important feedbacks between these processes in the geomorphic model the largest channel in each 4 4 km cell is explicitly treated the channel incision being driven by a stream power rule hillslopes internal to each cell respond rapidly to incision of the local channel prompting their treatment in the model as steady state forms i present analytic expressions for the local relief which is controlled by the local channel incision rate and rate constants associated with the dominant hillslope process either diffusive or landsliding initial conditions include any preexisting topography and a lightly etched a channel network the model is illustrated using the santa cruz mountains california i show that an earlier hypothesis that the santa cruz mountains are due to advection of topography past an uplift source related to a restraining bend in the san andreas fault remains viable when more specific geomorphic processes are considered the local tectonics are represented by crustal thickening necessitated by conservation of mass in the bend right lateral translation of crust with respect to the bend and flexural response to the distributed load the model produces reasonable geographic and statistical distributions of topography using rates of tectonic and geomorphic processes that are within the range of those measured locally this argues that this restraining bend is a long lived feature of the san andreas fault the slightly higher crest and shorter length of the southern santa cruz mountains may potentially be explained by slightly faster slip of the crust west of the fault with respect to the bend than of that to the east deflection is minimal beneath these relatively small mountains disallowing the interesting feedback of erosionally driven uplift the predicted pattern of exhumation could be used to guide the search for fission track sites that could aid in the testing of the model

middle paleolithic occupation on a marine isotope stage 5 lakeshore in the nefud desert saudi arabia major hydrological variations associated with glacial and interglacial climates in north africa and the levant have been related to middle paleolithic occupations and dispersals but suitable archaeological sites to explore such relationships are rare on the arabian peninsula here we report the discovery of middle paleolithic assemblages in the nefud desert of northern arabia associated with stratified deposits dated to 75 000 years ago the site is located in close proximity to a substantial relict lake and indicates that middle paleolithic hominins penetrated deeply into the arabian peninsula to inhabit landscapes vegetated by grasses and some trees our discovery supports the hypothesis of range expansion by middle paleolithic populations into arabia during the final humid phase of marine isotope stage 5 when environmental conditions were still favorable

weathering processes on the rock surface in natural outcrops the case of an ancient marble quarry belevi turkey weathering and mineralogical processes observed in a marble quarry in turkey are compared with similar processes occurring on monument surfaces patina formations microstromatolitic microlaminated monolayered as well as destructive processes mainly biopitting and bioerosion are associated with microbial colonisation of the rock surfaces and one influenced by microclimatic conditions patina stratification is independent of substrate rock but is affected by the position and orientation of rock surfaces the different layers formed by mineralisation processes may reflect the seasonality of climatic events and the consequent colonisation bio deteriorative processes take place mainly when the climatic conditions cause the organisms to live below the surface

stemflow influences on the formation of solution pipes in bermuda eolianite abstract soil filled pipes consisting of calcite casings were found in all of the eolianite formations of bermuda except the rocky bay formation the pipes are cylindrical in shape taper vertically downwards and occur in aggregated clusters they are most commonly exposed in areas of shoreline erosion in the form of soil filled cylindrical rims of calcite projecting up from the surrounding host eolianite in the early literature on the geology of bermuda it was suggested that these features were fossilized stumps of the bermuda palmetto tree sabal bermudiana in the study presented here this hypothesis is rejected on the basis of the morphology and stratigraphic position of these geomorphic features and their basal area and areal density compared with existing natural stands of s bermudiana the soil filled pipes of bermuda however cannot be simply explained as random solutional features that correspond to points where percolating soil water happened to converge and cause localized subsurface dissolution in situ measurements of stemflow from indigenous tree species suggest that the soil filled solution pipes of bermuda may be the product of stemflow drainage from particular tree species stemflow from s bermudiana was the most acidic with ph values as low as 4 29 compared to the gross rainfall in the open which had a ph of 5 58 the crowns of the bermuda cedar juniperus bermudiana and the subtropical tree species eugenia axillaris had the most significant funnelling effect stemflow volumes from individual trees representing these two species were 20 times greater than the volume of water that would have been collected in rain gauges with orifice areas equivalent to the trees trunk basal areas tree species capable of acidifying intercepted rainwater and funnelling large quantities down their trunks as stemflow may be the cause of subsurface dissolution loci extending vertically downward through bermuda s soluble eolianite formations stemflow from long lived trees representing these species could account for the diameters the cyclindrical shape the vertical orientation and the soil filled interiors of the pipes successive generations of these trees in preferred habitats could explain their clustered distribution and high areal densities 103 pipes ha

automated georeferencing and orthorectification of amazon basin wide sar mosaics using srtm dem data frequently large synthetic aperture radar sar mosaics are not precisely georeferenced because topographic distortions are not removed during the mosaicking process due to the lack of adequate digital elevation models dems the shuttle radar topography mission srtm has recently provided high resolution dem data with nearly global coverage and makes it possible to rectify sar mosaics though techniques are available for rectifying individual scenes of sar imagery using dem data these methods encounter difficulties when rectifying sar mosaics because abrupt geometric discontinuities occur in sar mosaics at scene boundaries this paper introduces an automated method to removing topographic distortions from sar mosaics and producing orthorectified mosaics without accessing original sar images the procedures include sar image simulation from dems two staged image matching between sar mosaics and the simulated image automated tie point derivation and screening piecewise image rectification for localized adjustment and production of orthorectified mosaics the method is used to orthorectify both high water and low water global rain forest mapping project sar mosaics covering the entire amazon basin validation results show that one pixel i e 92 m positioning accuracy root mean square error was achieved in both cases compared to 14 16 pixel errors i e 1288 1472 m of the original mosaics

estimation of supraglacial debris thickness using a novel target decomposition on l band polarimetric sar images in the tianshan mountains debris is widely distributed in the ablation zones of mountain glaciers in the tianshan mountains supraglacial debris can accelerate or hamper glacier ablation depending on its thickness thus it plays an important role in the mass balance of debris covered glaciers this paper proposes a novel method to estimate supraglacial debris thickness by using l band polarimetric synthetic aperture radar a new model based target decomposition is used to extract the surface scattering double bounce and volume scattering components the surface scatter model uses the extended bragg scatter which considers the depolarization effect for rough surfaces the volume scatter model uses elliptical scatterers which approximate the shape of the solids in the debris the volume scattering power is related to the dielectric properties of the debris the radar wavelength the incidence angle and the elliptical scatter shape once the target decomposition is performed the debris thickness can be inverted from the volume scattering power and other known parameters through comparison with a large number of field measurements the inversion is shown to be reasonable and the accuracy is validated to be 0 12 m based on the inversion map in the study area the debris thicknesses of the koxkar glacier and its neighboring glaciers are presented and analyzed

erosion thresholds and land surface morphology we propose a graphical technique to analyze the entirety of landforms in a catchment to define quantitatively the spatial variation in the dominance of different erosion processes high resolution digital elevation data of a 1 2 km2 hilly area where the channel network had been mapped in the field were used in the digital terrain model topog to test threshold theories for erosion the land surface was divided into 20 m2 elements whose shapes were then classified as convergent planar or divergent the entire landscape plotted on a graph of area per unit contour length against surface gradient shows each planform plotting as a separate field a simple steady state hydrologic model was used to predict zones of saturation and areas of high pore pressure to mimic the extreme hydrologic events responsible for erosive instability of the land surface the field observation that saturation overland flow is rare outside convergent zones provided a significant constraint on the hydrologic parameter in the model this model was used in threshold theories to predict areas of slope instability and areas subject to erosion by saturation overland flow both of which can contribute to channel initiation the proportion of convergent elements predicted to exceed the threshold varies greatly with relatively small changes in surface resistance demonstrating a high sensitivity to land use such as cattle grazing overall the landscape can be divided using erosion threshold lines into areas prone to channel instability due to runoff and stable areas where diffusive transport predominates

the southern hemisphere westerlies in the australasian sector over the last glacial cycle a synthesis abstract the southern hemisphere westerlies in the southwest pacific are known to have waxed and waned numerous times during the last two glacial cycles though even semi continuous histories of the westerlies extend back no more than about 20 000 years we have good evidence for at least three scales of events a westerly maximum occurs at the last glacial maximum there is less conclusive evidence for another westerly maximum in the late holocene and for a minimum at ca 11 ka it is too early to ascribe even a cycle to these data but there are grounds to suggest that milankovitch precessional forcing may underlie the observed pattern there is also a quasi 2600 year cycle present in antarctic ice cores that appears to correlate to variation in westerly flow there is strong centennial scale variability in historical times the little ice age lia ca 1400 1850 was associated with a poleward shift in the circumpolar trough in the southern ocean strengthened westerly circulation over tasmania and a strengthening of southwesterly circulation and neoglaciation in southern new zealand while the preceding period 800 1400 ad was less certainly marked by reduced westerly flow from modern records we know that decadal and inter annual variability is important e g pacific decadal oscillation high latitude mode also known as the antarctic oscillation el nino southern oscillation only a minority of the proxies examined can identify changes on these temporal scales but data from tree rings ice cores and laminated lake sediments do indicate systematic changes in these phenomena through time rossby wave patterns are shown to play a critical role in long duration events as well as at the synoptic scale we conclude that westerly circulation is as strong now as at any time in the last glacial cycle in addition changes in latitudinal boundaries in the westerlies may be nearly as large in inter annual zonal shifts ca 2 maximum as in glaciation interglaciation movements ca 3 4 there is however reasonable evidence of strengthening weakening across much of the westerly belt at westerly maxima minima such as the lia early holocene

the quaternary marine terraces of santa cruz california evidence for coseismic uplift on two faults the coast parallel elevation pattern of marine terraces along 50 km of coast centered about santa cruz california provides an opportunity to assess the relative roles of candidate uplift mechanisms we assemble 130 existing latitude longitude elevation inner edge locations from three of these marine terraces to constrain elastic dislocation models of coseismic uplift uplift resulting from repeated oblique slip seismic events similar to the loma prieta earthquake m s 6 9 of october 17 1989 appears to explain well the portion of the terrace uplift pattern south of santa cruz depending on whether the lowest terrace is assumed to correspond to isotope stage 5c or 5e the calculated mean repeat time for loma prieta events is either 490 or 820 yr corresponding to either 4 1 or 2 4mm yr slip rates on the loma prieta fault residual uplift not explained by such events increases monotonically to the north toward ano nuevo where the san gregorio fault zone intersects the coastline we assess whether this residual uplift may result from repeated events on the san gregorio fault given only the strike of the san gregorio fault we use an extensive parameter search to determine the geometry of and the style of motion on the implied rupture plane that best explains this residual uplift the fault parameters that minimize the misfit between data and model imply activity of a moderately steep 70 north east dipping san gregorio fault that ruptures in oblique thrust slip from 15 km to the surface the thrust slip component dominates the uplift pattern resulting in uplift of the coastline from santa cruz northward these parameters match available geological geodetic and seismic data on the dip and sense of motion on strictures within the san gregorio fault zone the san gregorio fault has therefore been an active late pleistocene participant in north american pacific plate boundary motion we conclude that the complex pattern of uplift along this 50 km reach of coastline can be explained by coseismic mechanisms tied to san andmas bend related fault structures onshore and to the san gregorio fault zone offshore as both of these mechanisms result locally in considerable shore normal uplift gradients caution is warranted in applying common correlation techniques based solely on uplift rates in the assignment of terrace ages in this and other such settings in addition while it is tempting to use terrace culmination offsets as a means of estimating san andreas fault dextral slip rates we provide a formalism to determine under what conditions such calculations are meaningful we conclude that the terrace offsets along the santa cruz coastline result not from dextral slip on the san andreas but from differential indentation of the loma prieta uplift pattern by the various sea level highstand coastlines

scarp degraded by linear diffusion inverse solution for age under the assumption that landforms unaffected by drainage channels are degraded according to the linear diffusion equation a procedure is developed to invert a scarp profile to find its diffusion age diffusion age having dimension length 2 is the product of diffusivity times chronological age the second moment of scarp slope grows linearly with age this fact together with an assumption about initial scarp shape allows the inverse determination of diffusion age age found assuming a vertical initial scarp is termed apparent age any nonvertical initial scarp profile has a nonzero initial apparent age true diffusion age differs from apparent age by a fraction of scarp offset squared the inverse procedure applied to synthetic data yields the following rules of thumb evidence of initial scarp shape has been lost when apparent age reaches twice its initial value if a scarp is formed by two events the inversion gives their offset weighted mean age with an error that is a fraction of offset squared a scarp that appears to have been formed by one event may have been formed by two with an interval between them as large as apparent age after scarps of two fault traces have diffused to appear as one the error in inferred age may be as large as half the apparent age variation of apparent age along strike would indicate multiple fault traces the simplicity of scarp profile measurement and this inversion makes profile analysis attractive if linearity of the flow law time for a free face to be reduced to the angle of repose and variation of diffusivity with climate and material could be established profile analysis would become a reliable dating technique

pseudobreccias revealed as calcrete mottling and bioturbation in the late dinantian of the southern lake district uk two types of pseudobreccia one with grey and the other with brown mottle fabrics occur in shoaling upward cycles of the urswick limestone formation of asbian late dinantian carboniferous age in the southern lake district uk the grey mottle pseudobreccia occurs in cycle base packstones and developed after backfilling and abandonment of thalassinoides burrow systems burrow infills consist of a fine to coarse crystalline microspar that has dull brown to moderate orange colours under cathodoluminescence mottling formed when an early diagenetic aerobic decay clock operating on buried organic material was stopped and sediment entered the sulphate reduction zone this probably occurred during progradation of grainstone shoal facies after which there was initial exposure to meteoric water microspar calcites then formed rapidly as a result of aragonite stabilization the precipitation of the main meteoric cements and aragonite bioclast dissolution post date this stabilisation event the brown mottle pseudobreccia fabrics are intimately associated with rhizocretions and calcrete which developed beneath palaeokarstic surfaces capping cycle top grainstones and post date all depositional fabrics although they may also follow primary depositional heterogeneities such as burrows they consist of coarse inclusion rich microspar calcites that are always very dull to non luminescent under cathodoluminescence sometimes with some thin bright zones these are interpreted as capillary rise and pedogenic calcrete precipitates the d 18 o values 5 to 8 pdb and the d 13 c values 2 to 3 pdb of the pseudobreccias are lower than the estimated d 18 o values 3 to 1 pdb and d 13 c values of 2 to 4 pdb of normal marine calcite precipitated from late dinantian sea water reflecting the influence of meteoric waters and the input of organic carbon

biological and physical evidence for extreme seasonality in central permian pangea climate models indicate increased desertification in the continental interior of pangea during the permian which would have affected the composition of the flora and fauna we present a multi proxy paleoenvironmental reconstruction of a terrestrial ecosystem in central pangea of lopingian age the reconstruction is based on biological and physical data from the moradi formation located in the tim mersoi sub basin northern niger paleosols and sedimentological evidence indicate that the prevailing climate was semi arid to very arid with marked intervals of high water availability carbon stable isotope data from organic matter and paleosols suggest that both the soil productivity and actual evapotranspiration were very low corresponding to arid conditions histological analysis of pareiasaur bones shows evidence of active metabolism and reveals distinct growth marks these interruptions of bone formation are indicative of growth rhythms and are considered as markers for contrasting seasonality or episodic climate events the macrofossil floras have low diversity and represent gymnosperm dominated woodlands most notable are ovuliferous dwarf shoots of voltzian conifers and a 25 m long tree trunk with irregularly positioned branch scars the combined biological and physical evidence suggests that the moradi formation was deposited under a generally arid climate with recurring periods of water abundance allowing for a well established ground water dependent ecosystem with respect to its environment this system is comparable with modern ecosystems such as the southern african namib desert and the lake eyre basin in australia which are discussed as modern analogues

rhizoliths in ancient eolianites abstract rhizoliths are abundant within permo pennsylvanian eolian rocks of southeastern utah they are also present at the tops of several eolian sand bodies within the pennsylvanian fountain formation of southeastern wyoming and at a single stratigraphic level within the jurassic navajo sandstone of southeastern utah ranging in diameter from less than 1 mm to 15 cm these cylindrical structures are composed of siliciclastic free micrite and calcite spar cylinders ramify throughout the uppermost 2 3 m of thin flat topped sand bodies large cylinders are compound rhizoliths and display alveolar fabric a feature resulting from rootlet calcification that is characteristic of modern and ancient calcretes development of rhizoliths required flat geomorphically stable substrates for plant growth highly permeable surficial sediments and sources of calcium ions the restriction of rhizoliths to planar deflation surfaces suggests that plants were unable to colonize or stabilize eolian bedforms paleozoic rhizoliths appear to be restricted to coastal areas with onshore winds associated evaporites suggest an arid to semi arid paleoclimate rhizoliths formed when carbonate allochems derived from an upwind epeiric sea were dissolved and calcite reprecipitated around plant roots quaternary rhizoliths are best developed in similar sedimentologic and geographic settings the abundance of rhizoliths and carbonate allochems in quaternary and late paleozoic low latitude coastal dunes suggests that they are genetically related to glacio eustatic sea level fluctuations

coseismic deformation and dislocation models of the 1989 loma prieta earthquake derived from global positioning system measurements global positioning system gps surveys were used to determine coseismic displacements within the epicentral region of the 1989 loma prieta earthquake near santa cruz the california highway department caltrans conducted the preearthquake survey in february and march 1989 using single frequency gps receivers in march 1990 we reoccupied eight of the caltrans stations using dual frequency receivers relative displacements were computed by differencing the station coordinates determined from these two surveys displacements were determined relative to sites remote from the earthquake by incorporating gps measurements from loma prieta station lp1 to the very long baseline interferometry vlbi site at fort ord examination of repeated measurements in the single frequency preearthquake survey indicates precision is 10 mm in the horizontal although it may be as low as 40 mm in the weakly connected part of the network the precision in the vertical is generally 30 40 mm in contrast the largest observed coseismic displacement is 410 mm horizontal and 341 mm vertical we use a quasi newton method to estimate the parameters of the uniform rectangular dislocation source that best fits the observed displacements the best fitting dislocation dips 68 southwest extending from 3 to 16 km depth strikes n66 w and has 1 8 m of dip slip and 1 2 m of strike slip the best fitting dislocation overlaps the aftershocks but is rotated 15 counterclockwise from the trend of the afterhock zone we find that the data can be fit nearly as well with a dislocation that is constrained to lie in the plane of the aftershocks in this case the fault extends from 5 to 15 km depth the constrained model explains 96 of the data both models have a moment of m0 2 9 1019 n m we also use the quasi newton method to estimate rectangular dislocation models from the leveling data of marshall et al 1991 and the trilateration and gps data of it lisowski et al 1990 in contrast to the previous studies we find that both of these data sets are independently best fit with dislocations embedded within the aftershock zone

distribution of calcrete in holocene coastal sands in relationship to climate southwestern australia seven study areas located over 320 km of coastal plain in southwestern australia show the distribution of groundwater and vadose calcrete within holocene coastal sands age 7 100 yr bp over a regional climate gradient the calcrete exhibits a range of structures that include rhizoconcretionary mottled massive and laminar types groundwater calcrete composed of mottled massive and laminar types occurs as a thin sheet in the zone of capillary rise just above the water table vadose calcrete is predominantly rhizoconcretionary at all sites where it is well developed the groundwater and vadose calcretes are closely associated with vegetation calcrete is well developed in southern areas that are humid further north as the rainfall decreases and evaporation increases calcrete is less common until it is absent or rare at the semiarid northern limit of the study region its limit of occurrence is correlated with a region whose rainfall is ca 800 mm annum evaporation is ca 1 900 mm annum and mean summer temperature is 23 degrees c this study shows therefore that a trend toward a drier climate may not be conducive to the development of calcrete although such a view prevails in the literature

paleosols in shallow marine carbonate sequences abstract shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations some ancient platform sequences contain hundreds of such surfaces associated with paleosols fossil soils typically calcretes a wide range of macro and microstructures are associated with these calcretes which are reviewed profile types and stages in profile development can be defined the nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate although hydromorphic effects related to marine flooding of the platforms can modify the paleosols a potentially important use of paleosols is to define the nature of sequence boundaries several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls

results from a new model of river basin evolution this paper briefly describes a model of the erosional development of catchments and their channel networks the model differentiates between the dominant transport processes in hillslope and channels the development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms the growth of a river basin is qualitatively described the model concepts are used to study the basin during periods of growth transient periods as well as during dynamic equilibrium this leads to hypotheses about the relationship between slopes relief tectonic uplift erodability runoff and catchment area it is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation

escarpment evolution on high elevation rifted margins insights derived from a surface processes model that combines diffusion advection and reaction experiments with a surface processes model of large scale 1 1000 km long term 1 100 m y erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent the model describes changes in topographic form as a result of simultaneous short and long range mass transport representing hillslope diffusive processes and fluvial transport advection respectively fluvial entrainment is modeled as a first order kinetic reaction which reflects the credibility of the substrate and therefore the fluvial system is not necessarily carrying at capacity one dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are 1 antecedent topography drainage 2 the timescale or equivalently a length scale in the fluvial entrainment reaction 3 the flexural response of the lithosphere to denudation and 4 the relative efficiencies of the short and long range transport processes when rainfall and substrate lithology are uniform a significant amount of discharge draining over the escarpment top causes it to degrade only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions an additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment this corresponds to a substrate that is hard to detach by fluvial erosion and therefore to fluvial erosion that is not transport limited continuous backtilting of an escarpment due to flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide it is essential if the escarpment gradient is to be preserved during retreat in a uniform lithology low flexural rigidities promote steep and slowly retreating escarpments for given rainfall and substrate conditions the morphology of a retreating model escarpment is determined by the ratio of the short range diffusive and long range advective transport efficiencies a low ratio which is interpreted to correspond to a relatively arid climate and weathering limited conditions promotes steep sharp topped escarpments with straight main slopes and escarpment retreat occurs over a wide range of height scales a high ratio interpreted to correspond to a more humid temperate climate produces a convex upper slope and concave lower slope morphology and only major escarpments are predicted to preserve a high scarp gradient lithological contrasts in the model produce more complex morphologies and predict the formation of scarps crowned by an erosionally resistant caprock however resistant caprocks are not an essential requirement for model scarps to retreat we conclude that the inferred controls and model behavior are both consistent with the present day morphology of rifted continental margins and with modern conceptual models of landscape evolution

the association of gold with calcrete abstract the discovery that au accumulates in calcrete pedogenic carbonate or caliche was made in 1987 by csiro calcrete is a general term describing accumulation of alkaline earth metals in soils of arid and semi arid terrains around the world the principal constituent of calcrete is calcite while au is a noble metal calcrete has been a significant tool in a number of au deposit discoveries so understanding the mechanisms by which these diametrically different components come together is valuable for enhancing future discovery numerous laboratory experiments case histories and exploration models have been published most from australia yet we do not fully understand the mechanisms involved it is timely therefore twenty five years on since the first publication of this phenomenon to review this highly unusual but economically important association critical to any review on au in calcrete is to first consider calcretes themselves the nature of a particular calcrete where it has formed and mode of formation is relevant to how where and why au accumulates within it this review commences with a background nomenclature history classification and some examples of calcrete types found near au deposits how calcretes form their origins and the role of biota is considered their locations in the regolith and landscape as well as exploration models for au in calcrete are discussed a section on the chemistry of au in calcretes details what we know about possible mechanisms of formation and considers what laboratory experiments on microorganisms and abiotic experiments tell us following on is a summary of practical aspects of identifying collecting and analysing samples for exploration purposes selected mineral exploration case histories are described and how they fit into models of exploration and different regolith settings concluding sections include a summary and implications of this accumulated knowledge to discovering au deposits