geochemistry of major and trace elements and pb sr isotopes of a weathering profile developed on the lower cambrian black shales in central hunan china abstract this paper reports a geochemical study on the major and trace elements and pb sr isotopes of a weathering profile developed in the lower cambrian black shales in central hunan china six weathering horizons were identified and sampled vertically throughout the profile the chemical composition of the profile consists of variable concentrations of the major elements fe2o3 feo mno mgo cao na2o and p2o5 and of less variable concentrations of sio2 tio2 al2o3 and k2o the chemical change caused by weathering is estimated by mass balance calculations and the results show that the element mobility is characterised by substantial loss of sio2 feo cao k2o na2o loi cr v ba cs rb sr u and th and moderate loss of al2o3 mgo fe2o3 ni cu pb tl sn sc ge and ree y the high field strength elements tio2 sn sc u ga ge zr hf nb and ta were immobile during weathering the chemical changes and the pb sr isotopic data suggest that four types of chemical reactions occurred the oxidation of sulphide minerals e g pyrite and organic carbon os the dissolution of less resistant clinochlore ia calcite and p bearing minerals dl the dissolution of detrital albite and microcline da and the transformation of clay tc minerals e g muscovite and illite smectite these chemical reactions then led to two stages of geochemical processes an early stage of chemical differentiation and a later stage of chemical homogenisation the chemical differentiation dominated by the os dl and da reactions led to the leaching of mobile elements e g mgo na2o k2o p2o5 sr and ree and the redistribution of some less mobile elements e g sio2 and al2o3 in contrast the chemical homogenisation which was caused by tc reactions led to the leaching of both mobile and less mobile elements from the system and ultimately transformed the weathered black shales into soil soils derived from black shales in south china might result from the above two geochemical processes

mobility of rhenium platinum group elements and organic carbon during black shale weathering this study investigates the effects of black shale weathering on the re os isotope system platinum group element concentrations and the degradation of organic matter samples from a weathering profile in late devonian 365 myr ohio shale show a pronounced decrease 77 in organic carbon corg near the present soil surface relative to the interior portion of the outcrop a similar trend is observed for total n 67 loss conversely organic phosphorus porg concentrations increase by 59 near the soil surface the decrease in corg is accompanied by a pronounced decrease in re 99 and to a lesser extent os 39 palladium and pt do not appear to be significantly mobile the effects of re and os mobility on the re os isotope system are significant none of the samples plots on a 365 myr isochron rather the samples define a trend with a slope corresponding to an age of 18 myr with an initial 187os 188os of 6 1 this indicates recent disturbance of the re os system isotope mass balance calculations imply that the labile fraction of os is significantly more radiogenic 187os 188os of 7 8 than the average of the unweathered samples 187os 188os of 6 4 based on data from this study the molar ratio of labile re to corg in ohio shale is estimated at 7 10 8 we estimate the present day riverine black shale derived re flux to seawater using literature data on re burial in anoxic marine sediments and assuming steady state between re release during black shale weathering and re burial in anoxic marine sediments then the labile re corg observed in this study implies that 0 5 tmol of corg is released annually from weathering of black shales a trace lithology in the continental crust this flux corresponds to 12 of the estimated annual co2 flux from oxidative weathering of sedimentary rocks the labile molar re os of 270 indicates that black shale weathering releases 130 mol os per year which accounts for 7 of the riverine os input to seawater the data from this study support the notion that the crustal cycles of labile corg re and os are tightly coupled gray shales which are less corg re and os rich but much more abundant in the continental crust than black shales are likely to be even more important continental sources of re and os to seawater

comparison of dynamic flow models for the central aleutian and tonga kermadec subduction zones using three dimensional 3 d instantaneous dynamic models of the central aleutian subduction zone we show that a low viscosity low density deltarho 10 kg m3 region in the wedge is needed to match observations of topography the geoid and the stress state in the slab and overriding plate previous models of the tonga kermadec subduction zone also require a low viscosity low density deltarho 20 kg m3 region in the wedge a low viscosity region in the wedge decouples the overriding plate from the downward flow in the wedge caused by the sinking slab reducing the magnitude of negative dynamic topography on the overriding plate and changing the state of stress in the slab from down dip tension to down dip compression if the low viscosity region is large as in the tonga kermadec models then the decoupling may also cause the overriding plate to go into extension these are the first dynamic models to simultaneously match the state of stress in the slab and overriding plate and suggest that the combination of stress state within the slab and overriding plate may provide an additional constraint on the viscosity structure within subduction zones

field test of autogenic control on alluvial stratigraphy ferris formation upper cretaceous paleogene wyoming internally generated autogenic sedimentary processes can obscure signals of tectonic movements climate conditions or sea level fl uctuations in alluvial basins the stratigraphic effects of autogenic dynamics have been considered negligible on time scales of 10 4 10 6 yr however recent physical and numerical models have shown that over basin fi lling time scales self organization in sedimentary systems can produce stratigraphic patterns similar to those resulting from changing basin boundary conditions here we present the fi rst fi eld based test for autogenic control on stratigraphy in an ancient alluvial basin the ferris formation upper cretaceous paleogene hanna basin wyoming is composed of clusters of closely spaced channel deposits separated by intervals dominated by overbank material a pattern that has been proposed as an example of a potentially autogenic stratigraphy in order to evaluate controls on ferris formation stratigraphy spatial patterns of key channel properties were analyzed these variables including sand body dimensions paleofl ow depth maximum clast size paleocurrent direction and sediment provenance were chosen because they can change in response to climate tectonic or sea level forcing and are commonly measurable in ancient alluvial successions no clear statistical trends were detected in the measured variables which suggests that external forces did not likely control stratigraphic organization in the unit this study demonstrates that autogenic dynamics in natural fi eld scale systems can produce organized stratigraphic patterns over much larger spatial and temporal scales than is typically presumed this fi nding emphasizes the need for further understanding of autogenic stratigraphy and greater care interpreting climate tectonic and eustatic changes from alluvial basins

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

biostratigraphic units and tectonism in mid cretaceous foreland of wyoming colorado and adjoining areas abstract chronolithologic units and unconformities in mid cretaceous formations of the central rocky mountains region indicate widespread marine transgressions and regressions as well as recurrent deformation of the foreland in the western interior during cenomanian turonian and coniacian times 88 96 ma the stratigraphic record of the widely recognized cenomanian and early turonian transgression middle turonian end page 856 regression and late turonian and coniacian transgression was modified in several areas by episodes of slight uplift and attendant erosion the most evident tectonism was in western montana during the middle to late cenomanian 93 94 ma in western wyoming and adjoining areas during the early turonian to earliest middle turonian 90 91 ma in north central colorado eastern wyoming and northwestern wyoming in the early late turonian 89 8 ma and in northeastern colorado wyoming and southwestern montana in the late late turonian 89 3 ma crestlines of most of the swells trend generally either northwest or northeast the tectonism of the mid cretaceous foreland corresponds in age to displacements of thrusts in the sevier orogenic belt of southwestern wyoming and southeastern id ho furthermore much of the foreland deformation probably reflects episodes of eastward thrusting in the thrust belt end of article last page 857

release of heavy metals during weathering of the lower cambrian black shales in western hunan china weathering of heavy metal enriched black shales may be one of the most important sources of environmental contamination in areas where black shales are distributed heavy metal release during weathering of the lower cambrian black shales lcbs in western hunan china was investigated using traditional geochemical methods and the icp ms analytical technique concentrations of 16 heavy metals 8 trace elements and p were measured for samples from selected weathering profiles at the taiping vanadium ore mine tp the matian phosphorous ore mine mt and taojiang stone coal mine tj the results show that the bedrock at these three profiles is enriched with sc v cr co ni cu zn pb th u mo cd sb tl and p based on mass balance calculation the percentages of heavy metals released in loss relative to immobile element nb were estimated the results show significant rates of release during weathering of v cr co ni cu zn u mo cd sn sb and tl for the tp profile sc cr mn co ni cu zn pb th cd and sn for the mt profile and sc mn co ni zn th cd sn and tl for the tj profile among these heavy metals co ni zn cd and sn show very similar features of release from each of the three weathering profiles the heavy metals released during weathering may affect the environment especially topsoil and surface waters and are possibly related to an observed high incidence of endemic diseases in the area

understanding the anomalous temperature data from the large block test at yucca mountain nevada 1 the large block test lbt at yucca mountain nevada is unique because of its size which is large enough to include a number of large fractures while still small enough so that boundary conditions and heterogeneities can be adequately controlled or characterized extensive mapping of the test block has established the presence of many small and large fractures preheat air injection testing has also revealed that the block is highly heterogeneous with fracture permeability varying more than four orders of magnitude we hypothesize that these large fractures and the resulting heterogeneity play a significant role in the development of coupled thermal hydrological th processes in the lbt a large volume of th data including temperature and saturation measurements has been collected from the lbt some of these temperature data from the lbt particularly those recorded by sensors tt1 14 and tt2 14 appear anomalous we show that these anomalous temperature data can be understood only if heterogeneity is invoked as an example we show that the heat pipe signature an indication of the extent of th coupling in tt2 14 is significantly longer in duration than that in tt1 14 we show that such a difference can be explained only if one includes a high permeability layer the existence of which has been indicated by air injection testing through the location of sensor tt2 14 similarly the oscillating temperature pattern in all sensors of borehole tt2 during 4470 4500 hours of heating is shown to be the result of rainwater flowing down a high permeability fracture the irregular temperature pattern in borehole tt1 happens because of rainwater reaching the source of heat quickly through a highly permeable inclined fracture and vapor rising upwards through a less permeable vertical fracture we also demonstrate that the anomalous temperature pattern recorded by tt1 14 during 2500 3500 hours of heating can be explained in terms of continuous upward movement of vapor and the downward flow of condensate through the fractures we conclude that the temperature data from the lbt are the results of coupled th processes occurring in a heterogeneous environment

effects of black shale weathering on the mobility of rhenium and platinum group elements radiogenic os from the continents dominates the late cenozoic marine os budget a variety of proposed radiogenic sources includes organic rich sediments precambrian shields and re rich sulfides identifying the dominant sources of radiogenic os to the oceans has a strong impact on past climate models because weathering of silicates acts as a net sink of co 2 whereas weathering of organic matter acts as a source here we investigate the effects of black shale weathering on the integrity of the re os isotope system and release of re and platinum group elements time correlative pairs of fresh drill core and weathered outcrop black shales of late ordovician age utica shale magnafacies quebec were analyzed for re os ir pt and pd as well as total s n and c as c carb and c org the results indicate that 25 64 of the initial re budget 45 90 of the os budget 14 65 of the ir budget 60 77 of the pt budget 69 86 of the pd budget and 44 96 of the c org budget are lost during weathering we use positive correlations of os pt and pd with c org and n to calculate the respective platinum group element concentrations in the unweathered organic matter end member as 3 ng g os 9 ng g pt and 11 24 ng g pd although black shales make up

a field study of the chemical weathering of ancient sedimentary organic matter weathering profiles developed on organic carbon rich black shales were studied to examine the loss and degradation of organic matter om during weathering and its role in the geochemical carbon cycle analysis of weathered shales reveals between 60 and nearly 100 total organic carbon toc loss in highly weathered samples relative to initial unweathered toc content pyrite loss coincides with or precedes organic carbon loss elemental analysis and flash pyrolysis gas chromatography py gc of kerogen concentrates indicate that there is little or no selective enrichment or depletion of norg containing sorg containing alkylaromatic branched alkyl or long chain n alkyl moieties in most profiles during weathering kerogen o c ratios consistently increase with toc and pyrite loss infrared spectroscopy ir reveals an increase in the relative abundance of c c and c o bonds relative to alkyl c h bonds in progressively weathered samples these results suggest a two component model for kerogen weathering largely non selective oxidation and hydration followed by cleavage dissolution of oxidized kerogen fragments the extent of weathering in a given outcrop is likely limited by a combination of the rate of physical erosion and exposure of the rock to oxidizing surface waters with om type composition playing a lesser role

the occurrence and dispersion of potentially toxic elements in areas covered with black shales and slates in korea abstract potentially toxic heavy metals together with other elements are present in some natural geological materials and the okchon black shale in korea provides an important example of this the dispersion of these elements in the rocks and soils derived from this shale are examined geochemical surveys were undertaken in 11 study areas in the okchon zone underlain by black shales slates phyllites and limestones after appropriate preparation of rocks and soils samples were analysed for multi elements by inaa icp aes and icp ms some potentially toxic elements are highly enriched in the okchon black shales and soils developed from these shales in the dukpyungri and majeonri areas in particular mean concentrations in soils in the dukpyungri area are 34 g g as 43 g g mo and 3 4 g g se which are significantly higher than the worldwide average for soils the degree of enrichment decreases in the order forest upland farm paddy playground soils and discriminant analysis by geochemical characteristics separates soils in the black shale area from those in other rock areas in terms of se zn mo and cd

location location location the variable lifespan of the laramide orogeny the laramide orogeny had a spatially variable lifespan which we explain using a geodynamic model that incorporates onset and demise of at slab subduction laramide shortening and attendant uplift began in southeast california usa at ca 90 ma swept to the northeast to arrive in the black hills of south dakota usa at ca 60 ma and concluded in south dakotawithin 10 m y during subsequent slab rollback the areal extent of laramide deformation decreased as the eastern edge of active deformation retreated to the southwest rapidly from ca 55 to 45 ma and more slowly from ca 45 to 40 ma with deformation ultimately ceasing in the southwestern part of the orogen at ca 30 ma geodynamic modeling of this process suggests that changes in the strength of the north america plate and densifcation of the farallon plate played important roles in controlling the areal extent of the laramide orogen and hence the lifespan of the orogenic event at any particular location in western north america

early cambrian ocean anoxia in south china the cause of the most marked changes in the evolution of life which define the first order stratigraphic boundary between the precambrian and the phanerozoic eon remains enigmatic and a highly topical subject of debate a global ocean anoxic event triggered by large scale hydrogen sulphide h 2 s release to surface waters has been suggested by wille et al on the basis of two data sets from south china and oman to explain the fundamental biological changes across the precambrian cambrian pc c boundary here we report a new precise shrimp u pb zircon age of 532 3 0 7 million years myr ago fig 1 for a volcanic ash bed in the critical unit that reflects the ocean anoxic event the lowermost black shale sequence of the niutitang formation in the guizhou province south china this age is significantly younger than the precise pc c boundary age of 542 0 0 3 myr ago approximately 10 myr younger than the extinction of the ediacaran fauna and thus challenging the view of a major ocean anoxic event having been responsible for the major changes in the direction of evolution at the pc c boundary

fault chronology and uplift history of the southern wind river range wyoming implications for laramide and post laramide deformation in the rocky mountain foreland the stratigraphy provenance and structural involvement of tectogenic sedimentary rocks along the southern and western margins of the wind river range in western wyoming record a complex laramide and later uplift history and identify the timing and position of individual faulting events the chronology of these events is 1 main uplift of the range by displacement on the wind river fault between 90 and 49 to 50 ma 2 the formation of reverse faults in the hanging wall of the wind river fault ca 50 to 51 ma 3 sagging of the toe of the wind river fault into sedimentary fill of the green river basin between 46 and 23 ma 4 uplift of the core of the range along reactivated precambrian shear zones between 30 and 23 ma and 5 collapse of the southern part of the range along normal faults beginning at 13 ma the sedimentary record of uplift and erosion indicates that erosion and basin fill kept pace or caught up with uplift so that by the end of the laramide there was little topographic relief between the crest of the range and the adjacent green river basin the present topography of the range characterized by a high level erosion surface and distinct crestal ridge derives from uplift of the erosion surface by the late laramide reverse faulting post laramide uplift of the crest of the range and neogene exhumation initial uplift of the range as early as 110 ma and prior to displacement on the wind river fault suggests either a pre laramide event of unknown origin or that laramide crustal shortening began nearly 35 m y earlier than commonly assumed

the many surface expressions of mantle dynamics plate tectonic theory suggests that present day topography can be explained by the repeated interactions between the tectonic plates moving along earth s surface however mounting evidence indicates that a significant proportion of earth s topography results from the viscous stresses created by flow within the underlying mantle rather than by the moving plates this dynamic topography is transient varying as mantle flow changes and is characterized by small amplitudes and long wavelengths it is therefore often hidden by or confused with the more obvious topographic anomalies resulting from horizontal tectonic movements however dynamic topography can influence surface processes and thus enter the geological record it has for example played a role in the establishment of amazon drainage patterns in turn surface processes such as the erosion of topographical anomalies could affect mantle flow this emerging view of dynamic topography suggests that the concept of plate tectonics as the driver of surface deformation needs to be extended to include the vertical coupling between the mantle and the surface unravelling this coupling back in time with the help of models and the geological record can potentially provide unprecedented insights into past mantle dynamics

simultaneous inversion of mantle properties and initial conditions using an adjoint of mantle convection through the assimilation of present day mantle seismic structure adjoint methods can be used to constrain the structure of the mantle at earlier times i e mantle initial conditions however the application to geophysical problems is restricted through both the high computational expense from repeated iteration between forward and adjoint models and the need to know mantle properties such as viscosity and the absolute magnitude of temperature or density a priori we propose that an optimal first guess to the initial condition can be obtained through a simple backward integration sbi of the governing equations thus lessening the computational expense given a model with known mantle properties we show that a solution based on an sbi generated first guess has smaller residuals than arbitrary guesses mantle viscosity and the effective rayleigh number are crucial for mantle convection models neither of which is exactly known we place additional constraints on these basic mantle properties when the convection induced dynamic topography on earth s surface is considered within an adjoint inverse method besides assimilating present day seismic structure as a constraint we use dynamic topography and its rate of change in an inverse method that allows simultaneous inversion of the absolute upper and lower mantle viscosities scaling between seismic velocity and thermal anomalies and initial condition the theory is derived from the governing equations of mantle convection and validated by synthetic experiments for both one layer viscosity and two layer viscosity regionally bounded spherical shells for the one layer model at any instant of time the magnitude of dynamic topography is controlled by the temperature scaling while the rate of change of topography is controlled by the absolute value of viscosity for the two layer case the rate of change of topography constrains upper mantle viscosity while the magnitude of dynamic topography determines the temperature scaling lower mantle viscosity when upper mantle lower mantle density anomaly dominates the flow field this two stage scheme minimizes the tradeoff between temperature and lower mantle viscosity for both cases we show that the theory can constrain mantle properties with errors arising through the adjoint recovery of the initial condition for the two layer model this error is manifest as a tradeoff between the temperature scaling and lower mantle viscosity

migration of dynamic subsidence across the late cretaceous united states western interior basin in response to farallon plate subduction backstripped cross sections of the late cretaceous succession across central utah colorado and southern wyoming in the western interior basin united states reveal a component of continuously evolving long wavelength residual subsidence in addition to subsidence driven by the sevier thrust belt and associated sediment loads the loci of maximum rates of this residual subsidence moved eastward from ca 98 to 74 ma in phase with the west to east passage of the farallon slab as reconstructed from tomography based on quantitative inverse models these new subsidence data allow testing of existing subduction models and confi rm the dynamic subsidence origin of the western interior basin furthermore regional variations in subsidence rates suggest a possible defi cit of negative buoyancy mantle loading inside the slab beneath colorado supporting the hypothesis that the thickened slab represents a subducted oceanic plateau this paper documents how the cretaceous stratigraphy records the timing patterns and position of underlying mantle processes during farallon slab subduction the new data also reveal patterns indicative of the commencement of the laramide orogeny in the western united states

the ups and downs of north america evaluating the role of mantle dynamic topography since the mesozoic the driving force for transient vertical motions of earth s surface remains an outstanding question a main difficulty lies in the uncertain role of the underlying mantle especially during the geological past here i review previous studies on both observational constraints and physical mechanisms of north american topographic evolution since the mesozoic i first summarize the north american vertical motion history using proxies from structural geology geochronology sedimentary stratigraphy and geomorphology based on which i then discuss the published physical models overall there is a progressive consensus on the contribution of mantle dynamic topography due to buoyancy structures associated with the past subduction at the continental scale a largely west to east migrating deformation pattern suggests an eastward translation of mantle dynamic effects consistent with models involving an eastward subduction and sinking of former farallon slabs since the cretaceous among the existing models the inverse model based on an adjoint algorithm and time dependent data constraints provides the most extensive explanations for the temporal changes of north american topography since the mesozoic at regional scales debates still exist on the predicted surface subsidence and uplift within both the western and eastern united states where discrepancies are likely due to differences in model setup e g mantle dynamic properties and boundary conditions and the amount of time dependent observational constraints toward the development of the next generation predictive geodynamic models new research directions may include 1 development of enhanced data assimilation capabilities 2 exploration of multiscale and multiphysics processes and 3 cross disciplinary code coupling

structural and sedimentological development of footwall growth synclines along an intraforeland uplift east central bighorn mountains wyoming structural sedimentological and provenance data from paleogene synorogenic deposits of the east central flank of the bighorn mountains provide new information about the development of footwall growth synclines the evolution of fault related folds and the erosional unroofing history of intraforeland uplifts three conglomerate units the upper conglomerate member of the fort union formation and the kingsbury and moncrief members of the wasatch formation are incorporated within an asymmetric east verging growth syncline in the footwall of the main range bounding thrust system three stages of footwall deformation are recorded within these conglomerates analysis of mapped progressive unconformities retrodeformed balanced cross sections and conglomerate clast composition data define these stages as part of a continuum of deformation associated with the development of footwall growth synclines development of an anticline syncline pair marked the earliest stage of growth syncline formation stage i rotation of the shared fold limb resulted in amplification of the growth syncline fine grained synorogenic sediment derived from easily eroded mesozoic mudstone bypassed the growth syncline during this stage by the end of lebo shale deposition an average of 12 1 of shortening and 6 46 km of uplift had occurred along the range margin continued growth syncline development was marked by the deposition of the kingsbury conglomerate the kingsbury conglomerate was derived from resistant middle and lower paleozoic carbonate strata in the uplifted source terrane intraformational unconformities recording as much as 55 of bed rotation were developed within the kingsbury conglomerate as fold limb rotation occurred coeval with deposition cross sections indicate that during this early stage of fault related folding an average of 16 9 shortening and 8 12 km of uplift occurred along the eastern flank of the bighorn mountains end of stage i the intermediate stage stage ii of footwall growth syncline development involved partial truncation of the growth syncline by the advancing thrust faults and deposition of the moncrief conglomerate the lower portion of the moncrief conglomerate was rotated basinward in the developing growth syncline the final stage of deformation stage iii was dominated by the thrust faulting of middle and lower paleozoic strata eastward over steeply dipping mesozoic strata and rotated eocene synorogenic conglomerate during this stage of deformation the moncrief conglomerate was deformed as the initially blind thrusts propagated into the near surface conglomerate deposits truncated the entire footwall syncline and overrode the synorogenic conglomerate package cross sections in areas where this final stage of deformation is well developed indicate that an average of 24 1 shortening and 9 7 km of uplift had occurred along the eastern margin of the bighorn mountains the caliber of synorogenic deposition in the powder river basin was linked directly to the lithologic composition of the bighorn mountains approximately half of the 3 6 km thick source stratigraphic section of the eastern bighorn mountains was eroded prior to accumulation of conglomerate the majority of this eroded material was derived from mesozoic mudstone and poorly indurated sandstone that were incapable of generating coarse detritus the first paleogene conglomerates deposited along the east central bighorn mountains therefore do not represent the initiation of laramide uplift but instead represent the exposure of coarse clast forming rock types from the lower half of the hanging wall stratigraphic section i e the mississippian madison limestone and ordovician bighorn dolomite

geochemistry of soils derived from black shales in the ganziping mine area western hunan china the geochemistry of major and trace elements including heavy metals and rare earth elements of the fresh and weathered black shales and the soils derived from black shales in the ganziping mine area in western hunan province china were studied using the following techniques x ray fluorescence xrf inductively coupled plasma mass spectrometer icp ms and x ray diffraction xrd the results show that the black shale soils are significantly enriched with al2o3 and fe2o3 and depleted of mobile elements cao na2o and k2o the soils are also highly enriched with heavy metals u v ni ba cu zn and pb that may cause potential heavy metal contamination of the soils composition of the soils is homogeneous compared to the weathered black shales for which the concentrations of major elements except cao and na2o and trace elements except heavy metals u v ni ba cu zn and pb as well as the mobile sr show lower variations than in the weathered black shales ratios of zr hf ta nb y ho nd sm and ti ti zr of the soils are also less variable with values constantly similar to that of the fresh and weathered black shales correspondingly thus components of the soils are believed to be contributed from the parent black shales through weathering and pedogenesis it is concluded that the soils were formed by at least two stages of geochemical processes the early stage of chemical differentiation and the later stage of chemical homogenization the chemical differentiation that was taken during black shale weathering might have caused the depletion of cao and na2o and the enrichment of al2o3 and fe2o3 while the chemical homogenization that was taken during pedogenesis led to the depletion of sio2 and k2o and to the further enrichment of al2o3 and fe2o3 the heavy metal enrichment contamination of the soils was then genetically related to the enrichment of al2o3 and fe2o3 in the soils

relative motions between oceanic plates of the pacific basin appendix tables are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b84 012 2 50 payment must accompany order relative motion poles describing the displacement histories between the pacific plate and once adjacent oceanic plates farallon kula izanagi i izanagi ii and phoenix were derived for the late mesozoic and cenozoic eras because fracture zone and magnetic anomaly data are generally available from the pacific plate but not from adjacent plates a new method of analysis for onesided data was required this analysis produced stage poles and rates of relative plate motion and estimates of their confidence regions the following are the main conclusions drawn from our analysis 1 for time intervals of the order of 107 years termed stages relative motion poles for plate pairs remained nearly fixed between stages shifts in poles were commonly both large and abrupt within stages rates of plate motion were commonly observed to change markedly indicating that plates changed speed more frequently than they changed direction 2 the relative motions of all of the plates analyzed changed at about chron m11 135 ma chron 34 85 ma and chron 25 56 ma 3 during the early cretaceous there were five oceanic plates in the pacific basin rather than the four recognized by previous workers 4 to determine the number of farallon plates that existed to the east of the pacific plate during the time interval from chron 34 85 ma to chron 25 56 ma fracture zones and magnetic anomalies that record pacific farallon spreading from the northern central and southern pacific plate were analyzed separately and collectively the analysis shows that a single pacific farallon relative motion pole and a single rate are consistent with all of the data 5 spreading rates along the pacific kula ridge decreased markedly between chrons 32b and 25 72 56 ma probably in response to the arrival of buoyant kula lithosphere at a subduction zone northwest of the bering sea 6 soon after chron 25 56 ma a major reorganization is recorded along the pacific farallon boundary the kula farallon boundary is also thought to have changed during this reorganization 7 kula pacific anomalies north of anomaly 25 are modeled by assuming continued kula pacific spreading after chron 25 56 ma 8 probably by chron 18 43 ma pacific kula spreading had ceased and the kula farallon ridge system had evolved into alignment with the pacific farallon spreading direction however the timing of these events is uncertain because pacific kula data younger than chron 25 56 ma are sparse

topographic asymmetry of the south atlantic from global models of mantle flow and lithospheric stretching the relief of the south atlantic is characterized by elevated passive continental margins along southern africa and eastern brazil and by the bathymetric asymmetry of the southern oceanic basin where the western flank is much deeper than the eastern flank we investigate the origin of these topographic features in the present and over time since the jurassic with a model of global mantle flow and lithospheric deformation the model progressively assimilates plate kinematics plate boundaries and lithospheric age derived from global tectonic reconstructions with deforming plates and predicts the evolution of mantle temperature continental crustal thickness long wavelength dynamic topography and isostatic topography mantle viscosity and the kinematics of the opening of the south atlantic are adjustable parameters in thirteen model cases model predictions are compared to observables both for the present day and in the past present day predictions are compared to topography mantle tomography and an estimate of residual topography predictions for the past are compared to tectonic subsidence from backstripped borehole data along the south american passive margin and to dynamic uplift as constrained by thermochronology in southern africa comparison between model predictions and observations suggests that the first order features of the topography of the south atlantic are due to long wavelength dynamic topography rather than to asthenospheric processes the uplift of southern africa is best reproduced with a lower mantle that is at least 40 times more viscous than the upper mantle

reconstructing farallon plate subduction beneath north america back to the late cretaceous using an inverse mantle convection model that assimilates seismic structure and plate motions we reconstruct farallon plate subduction back to 100 million years ago models consistent with stratigraphy constrain the depth dependence of mantle viscosity and buoyancy requiring that the farallon slab was flat lying in the late cretaceous consistent with geological reconstructions the simulation predicts that an extensive zone of shallow dipping subduction extended beyond the flat lying slab farther east and north by up to 1000 kilometers the limited region of flat subduction is consistent with the notion that subduction of an oceanic plateau caused the slab to flatten the results imply that seismic images of the current mantle provide more constraints on past tectonic events than previously recognized

lacustrine and fluvial deltaic depositional systems fort union formation paleocene powder river basin wyoming and montana the powder river basin is a laramide foreland basin that was filled by a combination of fluvial deltaic paludal and lacustrine sediments the depositional history of the fort union formation was unraveled in a regional subsurface study using data from approximately 1 400 geophysical well logs the depositional model developed from the subsurface study was tested by selective fieldwork the powder river basin originated as a structural and depositional basin in earliest middle paleocene as a result of rapid subsidence a lake lake lebo formed along the basin axis lake lebo documented in the mudstone of the lebo shale member spread rapidly to cover an area greater than 10 000 mi2 25 900 km2 during the middle through late paleocene lake lebo was filled peripherally by fluvial deltaic systems that are recorded in the coarser clastics of the tongue river member primary basin fill was from 1 the eastern margin by elongate deltas fed by suspended to mixed load fluvial systems issuing from the ancestral black hills and 2 the southwestern margin by mixed to bed load streams emanating from the wind river basin secondary fill was from th northwest by an elongate delta system fed by a suspended to mixed load fluvial system flowing from the bull mountain basin

distinguishing middle late cretaceous tectonic events from regional sea level change using foraminiferal data from the u s western interior foraminiferal data from seven stratigraphic sections between the utah wyoming thrust belt and western kansas record 13 correlatable paleoecologic events between coniacian and early campanian time and provide a framework for interpreting tectonic timing and regional sea level changes at least three events are synchronous within available biostratigraphic resolution we infer that the events are regionally isochronous and result from short term that the 13 paleoecologic events are observed across the foreland basin indicates that from western kansas to the sevier thrust belt the rate of change of sea level was sufficiently rapid to exceed the rate of sea floor sedimentation in the case of sea level rise and the maximum rate of basin subsidence in the case of sea level fall the recognition of these events suggests that correlatable sea level changes that are found within and beyond the flexural wavelength of foreland basins can be used to distinguish tectonic events from regional sea level changes the recognition of relatively short term subsidence events indicates that tectonic events can occur in foreland basins on time scales similar to third order or possibly higher eustatic sea level changes although this study examines only data from the u s western interior the technique of using high resolution subsidence analysis to identify asymmetric subsidence promises to aid in identifying the tectonic component of subsidence in other foreland basin settings

density of morb eclogite in the upper mantle in order to study the role of eclogite subducted oceanic crust in geodynamics we carried out high pressure experiments on natural mid oceanic ridge basalt morb using a multi anvil apparatus we determined phase relations of morb as a function of pressure and temperature in the temperature range of 1200 1700 c and pressures from 5 to 14 gpa the present results differ from a previous high pressure study of morb earth planet sci lett 77 1986 245 conducted at 1200 c as follows 1 coesite coe or stishovite st appears throughout the studied pressure range and 2 the clinopyroxene garnet cpx gar ratio is smaller particularly in the low pressure range 12 gpa our results show that the calculated bulk density of subducted oceanic crust increases discontinuously at around 9 gpa due to the coesite stishovite phase transition the density is considerably higher than estimates based on the previous experiments at pressures less than 12 gpa thus the role of eclogite in driving subduction should be more important than previously thought on the other hand the density difference between peridotite and eclogite in ascending mantle plumes becomes smaller as temperature increases a result of the increase in clinopyroxene garnet sio2 ratio in eclogite with increasing temperature as eclogite is still denser than peridotite even under subsolidus conditions recycled oceanic crust entrained in ascending plumes must be sustained by the upward flow of ambient peridotite in mantle plumes

weathering of the new albany shale kentucky usa i weathering zones defined by mineralogy and major element composition abstract comprehensive understanding of chemical and mineralogical changes induced by weathering is valuable information when considering the supply of nutrients and toxic elements from rocks here minerals that release and fix major elements during progressive weathering of a bed of devonian new albany shale in eastern kentucky are documented samples were collected from unweathered core parent shale and across an outcrop excavated into a hillside 40 year prior to sampling quantitative x ray diffraction mineralogical data record progressive shale alteration across the outcrop mineral compositional changes reflect subtle alteration processes such as incongruent dissolution and cation exchange altered primary minerals include k feldspars plagioclase calcite pyrite and chlorite secondary minerals include jarosite gypsum goethite amorphous fe iii oxides and fe ii al sulfate salt efflorescence the mineralogy in weathered shale defines four weathered intervals on the outcrop zones a c and soil alteration of the weakly weathered shale zone a is attributed to the 40 a exposure of the shale in this zone pyrite oxidization produces acid that dissolves calcite and attacks chlorite forming gypsum jarosite and minor efflorescent salt the pre excavation active weathering front zone b is where complete pyrite oxidation and alteration of feldspar and organic matter result in increased permeability acidic weathering solutions seep through the permeable shale and evaporate on the surface forming abundant efflorescent salt jarosite and minor goethite intensely weathered shale zone c is depleted in feldspars chlorite gypsum jarosite and efflorescent salts but has retained much of its primary quartz illite and illite smectite goethite and amorphous fe iii oxides increase due to hydrolysis of jarosite enhanced permeability in this zone is due to a 14 loss of the original mass in parent shale denudation rates suggest that characteristics of zone c were acquired over 1 ma compositional differences between soil and zone c are largely attributed to illuvial processes formation of additional fe iii oxides and incorporation of modern organic matter

trace metals distribution from a serpentinite weathering at the scales of the weathering profile and its related weathering microsystems and clay minerals the distribution of four trace metals nickel ni chromium cr manganese mn and cobalt co and some major elements is studied in a soil profile derived from a natural trace metals bearing rock serpentinite at the scales of 1 the weathering profile c and b horizons and 2 its related weathering microsystems and clay minerals all trace elements are relatively enriched in weathered horizons compared to the rock in the same way as iron and aluminium whereas magnesium is largely leaching an evolutive sequence of trace metals host phases is formed along the weathering profile from magnesian at the bottom to iron rich clay minerals and then aluminous clay minerals and oxy hydroxides at the top different chemical forms of trace metals in weathering profile have been quantified by chemical extractions ni and cr remain mainly in the silicates in contrast mn and co are mainly distributed into amorphous oxy hydroxides in addition trace metals contents are measured using electron microprobe in individual rock forming minerals and in their specific weathering microsystem each with its specific clay mineral each rock forming mineral serves as the host phase for a specific trace metal silicates serpentine and clinochlore contain cr ni and mn whereas oxides concentrate co and cr in the first weathering stages ni and cr are concentrated in secondary clays especially in fe montmorillonite derived from mesh serpentine minerals and in trioctahedral vermiculite derived from chlorite respectively whereas mn and co are mainly used to constitute secondary oxides at the top of the profile mn co and ni host secondary oxy hydroxides have developed due to iron segregation

multiphysics processes in partially saturated fractured rock experiments and models from yucca mountain 1 the site investigations at yucca mountain nevada have provided us with an outstanding data set one that has significantly advanced our knowledge of multiphysics processes in partially saturated fractured geological media such advancement was made possible foremost by substantial investments in multiyear field experiments that enabled the study of thermally driven multiphysics and testing of numerical models at a large spatial scale the development of coupled process models within the project have resulted in a number of new advanced multiphysics numerical models that are today applied over a wide range of geoscientific research and geoengineering applications using such models the potential impact of thermal hydrological mechanical thm multiphysics processes over the long term e g 10 000 years could be predicted and bounded with some degree of confidence the fact that the rock mass at yucca mountain is intensively fractured enabled continuum models to be used although discontinuum models were also applied and are better suited for analyzing some issues especially those related to predictions of rockfall within open excavations the work showed that in situ tests rather than small scale laboratory experiments alone are essential for determining appropriate input parameters for multiphysics models of fractured rocks especially related to parameters defining how permeability might evolve under changing stress and temperature a significant laboratory test program at yucca mountain also made important contributions to the field of rock mechanics showing a unique relation between porosity and mechanical properties a time dependency of strength that is significant for long term excavation stability a decreasing rock strength with sample size using very large core experiments and a strong temperature dependency of the thermal expansion coefficient for temperatures up to 200 c the analysis of in situ heater experiments showed that fracture closure opening caused by changes in normal stress across fractures was the dominant mechanism for thermally induced changes in intrinsic fracture permeability during rock mass heating cooling and that fracture shear dilation appears to be less significant significant effort was devoted to predicting the long term stability of underground excavations under mechanical strength degradation and seismic loading perhaps one of the most challenging tasks within the project we note that such long term strength degradation is actually an example of a chemically mediated process governed by underlying microscopic stress corrosion and chemical diffusion processes in the yucca mountain project such chemically mediated mechanical changes were considered implicitly through model calibrations against laboratory and in situ heater experiments at temperatures anticipated to be experienced by the rock a possible future research direction would be to simulate such processes mechanistically in a complete coupled thmc framework where c denotes chemical processes

unroofing incision and uplift history of the southwestern colorado plateau from apatite u th he thermochronometry the source of buoyancy for the uplift of cratonic plateaus is a fundamental question in continental dynamics the 1 9 km uplift of the colorado plateau since the late cretaceous is a prime example of this problem we used apatite u th he thermochronometry 230 analyses 36 samples to provide the fi rst single system regional scale proxy for the unroofi ng history of the southwestern quadrant of the plateau the results confi rm overall southwest to northeast unroofi ng from plateau margin to plateau interior a single phase of unroofi ng along the plateau margin in late cretaceous to early tertiary sevierlaramide time contrasts with multiphase unroofi ng of the southwestern plateau interior in early and mid to late tertiary time the early cretaceous was characterized by northeastward tilting and regional erosion followed by aggradation of 1500 m of upper cretaceous sediments along the eroded plateau margin sevier laramide denudation affected the entire southwestern plateau was concentrated along the plateau margin and migrated from northwest to southeast following a period of relative stability of the landscape from ca 50 30 ma signifi cant unroofi ng of the southwestern plateau interior occurred between ca 28 and 16 ma additional denudation north of the grand canyon took place in latest tertiary time mid tertiary dates from the grand canyon basement at the bottom of the upper granite gorge limit signifi cant incision of the modern grand canyon below the kaibab surface to 1500 m difference in vertical structural position if these models are correct they indicate that a proto grand canyon of kilometer scale depth had incised post paleozoic strata by the early eocene evidence for kilometerscale mid tertiary relief in northeast fl owing drainages along the plateau margin as well as the mid tertiary episode of plateau interior unroofi ng imply that the southwestern plateau interior had attained substantial elevation by at least 25 20 ma if not much earlier these observations are inconsistent with any model calling for exclusively late tertiary uplift of the southwestern plateau sevier laramide plateau surface uplift and incision thus result from one or more processes that enhanced the buoyancy of the plateau lithosphere expanding the cordillera s orogenic highlands into its lowstanding cratonic foreland the onset of the laramide slab s demise at ca 40 ma and the major pulse of extension in the basin and range from ca 16 10 ma appear to have had little infl uence on the denudation history of the southwestern plateau in contrast the post laramide unroofi ng episodes may be explained by drainage adjustments induced by rift related lowering of regions adjacent to the plateau without the need to otherwise modify the plateau lithosphere our data do not preclude a large component of post early eocene elevation gain or the geodynamic mechanisms it may imply but they do point toward laramide age buoyancy sources as the initial cause of signifi cant surface uplift ending more than 500 m y of residence near sea level

modeling of thermally driven hydrological processes in partially saturated fractured rock 1 this paper is a review of the research that led to an in depth understanding of flow and transport processes under strong heat stimulation in fractured porous rock it first describes the anticipated multiple processes that come into play in a partially saturated fractured porous volcanic tuff geological formation when it is subject to a heat source such as that originating from the decay of radionuclides the rationale is then given for numerical modeling being a key element in the study of multiple processes that are coupled the paper outlines how the conceptualization and the numerical modeling of the problem evolved progressing from the simplified to the more realistic examples of numerical models are presented so as to illustrate the advancement and maturation of the research over the last 2 decades the most recent model applied to in situ field thermal tests is characterized by 1 incorporation of a full set of thermal hydrological processes into a numerical simulator 2 realistic representation of the field test geometry in three dimensions and 3 use of site specific characterization data for model inputs model predictions were carried out prior to initiation of data collection and the model results were compared to diverse sets of measurements the approach of close integration between modeling and field measurements has yielded a better understanding of how coupled thermal hydrological processes produce redistribution of moisture within the rock which affects local permeability values and subsequently the flow of liquid and gases the fluid flow in turn will change the temperature field we end with a note on future research opportunities specifically those incorporating chemical mechanical and microbiological factors into the study of thermal and hydrological processes

far traveled latest cretaceous paleocene conglomerates of the southern rocky mountains usa record of transient laramide tectonism a solitary thin widespread conglomerate is found in latest cretaceous paleocene sections in each of these laramide basins of the southern rockies the table cliff northwestern kaiparowits plateau and uinta basin utah the piceance creek and denver basins colorado and the san juan basin new mexico these units are unusual compared to typical syntectonic conglomerates in that they occur as a thin interval underlain by a disconformity are far traveled across most of the length of their basins generally reflect a change in dispersal direction relative to underlying deposits and were deposited during a period of reduced subsidence all units were deposited well after local initiation of the laramide orogeny but within 8 m y of each other however each conglomerate unit was separately derived from individual source areas and is not part of a once continuous gravel sheet similar widespread conglomerate units of this age are apparently absent in other rocky mountain laramide basins previous studies postulate the shallow subduction of an oceanic plateau the conjugate shatsky rise beneath the u s cordillera during the time interval of conglomerate deposition the distribution timing and dispersion directions of the far traveled conglomerates are grossly consistent with vertical motions and surface tilting along the transport path of the oceanic plateau an exact match of conglomerate timing differs from previously proposed models but uncertainties in timing of deposits and the lack of constraints on the shape and structure of the subducted plateau preclude our ability to further refine the comparison elsewise local tectonic activity climate change and sea level fluctuations fail to explain the observed spatiotemporal pattern hence we suggest that these deposits record a transient mantle derived tectonic effect traversing the rocky mountain region and demonstrate the utility of stratigraphy as a record of subtle tectonic events

dynamic versus flexural controls of late cretaceous western interior basin usa the united states cretaceous western interior basin has long been considered a foreland basin driven by the sevier thrust and associated basin sediment loads however flexural studies demonstrate that this effect exists only within a narrow band in front of the thrust belt most of the basin appears to be due to mantle flow induced dynamic subsidence associated with farallon plate subduction here we show how the components of evolving long wavelength dynamic subsidence and flexural subsidence created the accommodation space and controlled the stratigraphy across the western united states based on a correlated stratigraphic section across central utah and colorado these backstripped subsidence data reveal the dynamic topography driven nature of the western interior basin the results seem to support that the depocenters track the trough of dynamic subsidence with ca 18 myr cycles through time and space and the stratigraphic patterns of large scale progradation eastward migration of depocenter and regional clinoform like downlap are related with the dynamic subsidence interpretation of these data also provides more insights into the repeated ca 2 to 6 myr cycles of thrust induced subsidence in front of the thrust belt which control the local eastward progradation of the sand bodies from the thrust belt the dynamic flexural subsidence and eustatic sea level changes interacted and controlled the timing and distribution of unconformities our work shows how the stratigraphy precisely records the timing patterns and position of dynamic versus flexural subsidences and that combination of such data leads to important geophysical discoveries and supplies strict constraints for geodynamic modeling

extreme enrichment of polymetallic ni mo pge au in lower cambrian black shales of south china an os isotope and pge geochemical investigation extreme metal enrichments occur in the lower cambrian niutitang formation a thick black shale sequence deposited on the yangtze platform of south china and form a regionally distributed conformable polymetallic ni mo pge au sulfide horizon the origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of re os isotopes and platinum group elements the black shales of the lower cambrian niutitang formation in guizhou province yielded an re os isochron age of 535 11 ma with an initial 187 os 188 os ratio of 0 80 0 04 which is similar to the initial 187 os 188 os ratio 0 78 0 19 of the ni mo sulfide ores but slightly lower than the initial 187 os 188 os ratio 1 18 0 02 of lower cambrian black shales from the lesser himalaya india a comparison of os isotope data among the chinese ni mo sulfide ores the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits the pge concentrations pt anomaly pt pt pt pd ir pd au pd ratios of the chinese ni mo sulfide ores are similar to those metal rich black shales of submarine volcanogenic hydrothermal origin from czech republic namibia and canada but are different from those data of the ocean floor fe mn crusts that have scavenged their pge and other metals directly from seawater it is therefore suggested that the ni mo sulfide ores from the niutitang black shale sequence in south china had a submarine hydrothermal origin the anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments the discharge of hydrothermal fluids into the cambrian ocean may have had a great effect on life during the cambrian explosion 2007 elsevier b v all rights reserved

late cretaceous subsidence in wyoming quantifying the dynamic component the late cretaceous western interior basin of north america is generally considered to have been a retroarc foreland basin flexural backstripping of the stratigraphic record from 97 2 ma to 73 4 ma along a section perpendicular to the wyoming idaho salient of the sevier belt clearly demonstrates that there were components of subsidence in addition to those driven by the thrust and associated sediment loads the simulation demonstrates that the flexural foredeep is only 180 120 km wide and shows a forebulge located near the subsequent laramide rock springs uplift foredeep strata between the rock springs uplift on the east and the thrust front to the west were mostly involved in the eastward overlapping thrust belt or deeply truncated by inferred rebound after 78 5 ma the difference between the observed decompacted cumulative subsidence and the amount of subsidence that can be explained by simple flexural loading the residual subsidence increases from 800 m in eastern wyoming to 1 8 km near the thrust belt the westward thickening upper cretaceous sediment wedge filled the accommodation space generated by downward tilting to the west of the north american cratonic margin by underplating and mantle flow associated with the shallowly subducted farallon plate

dynamic topography and vertical motion of the u s rocky mountain region prior to and during the laramide orogeny dynamic topography of earth s surface occurs in response to hydrodynamic stresses due to mantle flow beneath a flexible lithosphere here we compare the predicted dynamic topography from an inverse convection model that includes flat slab subduction with the known geologic history of the western united states from late cretaceous through paleocene time to evaluate the validity of the model results downwarping behind the evolving cordilleran volcanic arc took place after its inception in late triassic time culminating in the formation of the western interior seaway in late cretaceous time subsidence behind arcs is a consistent prediction of most models of dynamic topography a more detailed convection model is evaluated here by comparing it to the geologic history of the central rocky mountain region from 100 to 50 ma the match of predicted and observed tectonic subsidence is good up until the time that local deformation by the laramide orogeny begins this is most likely due to local flexural effects of mountain building overwhelming regional dynamic effects maps for successive time intervals show that the model matches the geologic history quite well through time and space in particular the subduction of the previously postulated oceanic plateau the conjugate shatsky rise has a significant impact on surface movements 1 from 95 to 88 ma the locations of most significant regional unconformities match the eastward migration of a zone of high topography 2 from 90 to 85 ma the zone of maximum subsidence coincides with the motion of the leading edge of the conjugate shatsky rise 3 from 78 to 60 ma the site of initiation of laramide deformation migrates coincidently with the position of the center of the conjugate shatsky rise 4 from 70 to 60 ma the time transgressive deposition of thin fluvial conglomerate units in the southern part of the study area is generally coincident with surface uplift caused by the trailing part of the conjugate shatsky rise these results suggest that the inverse model approximates the vertical motion history quite well synchroneity of the position of the center of the passing conjugate shatsky rise the landward limit of the evolving cordilleran volcanic arc and the initiation of laramide deformation suggests that the farallon plate became coupled with the overlying north american plate as the subducted oceanic plateau passed beneath progressively enhanced mechanical coupling between the plates was likely the impetus for laramide shortening this comparison of model results with surface geologic history provides a means to validate but not verify predictions of dynamic mantle flow models

phanerozoic marine inundation of continents driven by dynamic topography above subducting slabs a spherical model of mantle flow constrained by the locations of trenches can be used to predict the dynamic topography of the earth s surface and hence the marine inundation of continents for past periods of high sea level the predicted geographical pattern of flooding correlates well with the geological record the high spatial correlation may result from increased plate velocities at these times leading to increased rates of subduction subsidence and inundation at convergent margins

the coupled release of ree and pb to the soil labile pool with time by weathering of accessory phases wind river mountains wy abstract rare earth element ree distributions and pb isotope compositions were explored in soils varying in age from ca 0 4 to 300 ka developed on moraines in the wind river mountains wyoming soil extracts 0 6 m hcl were used to examine the soil labile pool while the major element distribution in soil profiles was used to determine the extent of weathering at different soil depths the results show that the chondrite normalized ree patterns of the deepest bulk soil within each profile reflects the composition of the moraine till except for the oldest soil up to ca 12 ka the soil extract fraction is enriched in light ree indicating early release of light ree to the soil labile pool while that of the two oldest soils are relatively enriched in heavy ree in the soil extracts the la sm ratio normalized to the deepest soil la d sm d decreases systematically with soil age similarly the eu anomaly in the deepest soil from each profile eu d eu d decreases slightly with soil age in the three young soils however eu d eu d increases with soil age in the older soils the systematic trends of these two ratios indicate the depletion of light ree in young soils and the enrichment of eu and heavy ree in the older soils based on the pb isotope ratios the relative contribution of pb to the soil labile pool via mineral weathering of u or th rich phases was assessed for the different stages of weathering the whole soil profile 208 pb 204 pb ratio was found to decrease with soil age and with la d sm d whereas it increased with the eu d eu d ratio in each horizon pb isotope ratios 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratio generally decrease with soil age in order to overcome possible effects from parent material heterogeneity the amount of radiogenic pb as compared to the whole soil composition was calculated and this was found to decrease systematically with soil age

was the laramide orogeny related to subduction of an oceanic plateau numerous models have been presented to explain the late cretaceous early cenozoic laramide orogeny which affected the foreland region of the western cordillera within the us1 the most attractive models invoke low angle subduction2 4 which can develop for various reasons5 6 evidence from south america indicates that one such reason may be the subduction of buoyant ocean floor we here extend the low angle subduction models by attributing the shallowing of the subduction angle during the laramide orogeny to subduction of a large oceanic plateau of anomalously thick and buoyant oceanic crust pacific plate history indicates that a twin to the hess rise may represent the oceanic plateau that triggered laramide events

chemical weathering of a soil chronosequence on granitoid alluvium ii mineralogic and isotopic constraints on the behavior of strontium the use of strontium isotopes to evaluate mineral weathering and identify sources of base cations in catchment waters requires an understanding of the behavior of sr in the soil environment as a function of time our approach is to model the temporal evolution of 87sr 86sr of the cation exchange pool in a soil chronosequence developed on alluvium derived from central sierra nevada granitoids during the past 3 ma with increasing soil age 87sr 86sr of ammonium acetate extractable sr initially decreases from values typical of k feldspar to those of plagioclase and hornblende and then remains constant even though plagioclase and hornblende are absent from the soils after approximately 1 ma of weathering the temporal variation of 87sr 86sr of exchangeable sr is modeled by progressively equilibrating sr derived from mineral weathering and atmospheric deposition with sr on exchange sites as waters infiltrate a soil column observed decreases in quartz normalized modal abundances of plagioclase hornblende and k feldspar with time and the distinct87sr 86sr values of these minerals can be used to calculate sr flux from weathering reactions hydrobiotites in the soils have nearly constant modal abundances chemistry and 87sr 86sr over the chronosequence and provide negligible sr input to weathering solutions the model requires time and soil horizon dependent changes in the amount of exchangeable sr and the efficiency of sr exchange as well as a biologic cycling term the model predicts that exchangeable sr initially has 87sr 86sr identical to that of k feldspar and thus could be dominated by sr leached from k feldspar following deposition of the alluvium the maximum value of 87sr 86sr observed in dilute stream waters associated with granitoids of the yosemite region is likewise similar to that of the k feldspars suggesting that k feldspar and not biotite may be the dominant source of radiogenic sr in the streams this study reveals that when attempting to use strontium isotopes to identify sources of base cations in catchment waters and biomass both preferential leaching of sr from minerals during incipient soil development and changing sr exchange efficiency must be considered along with chemical contributions due to mineral dissolution

quantification of loss of calcite pyrite and organic matter due to weathering of toarcian black shales and effects on kerogen and bitumen characteristics abstract comparison of geochemical data on posidonia shale early toarcian from a shallow unweathered core and from adjacent weathered exposures of the same fades was performed results revealed that quantitatively the most affected petrographic constituent is pyrite and that organic matter and carbonate were also altered by weathering due to this process of weathering the bulk composition of organic matter especially the molecular composition of soluble organic matter and the fluorescence colour of organic particles are changed estimates of weathering rates reveal that the annual release of sulphur and organic carbon from black shales may significantly add to anthropogenic pollution

paleogeographic and paleotectonic setting of laramide sedimentary basins in the central rocky mountain region in the rocky mountain region between central montana and central new mexico sedimentologically isolated nonmarine basins were produced by basement deformation during the laramide orogeny within the area formerly occupied by a broad late cretaceous foreland basin in which laterally continuous marine facies had accumulated previously laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere laramide basins include perimeter basins along the cratonic periphery of the arcuate laramide province axial basins along a north south intramontane trend and ponded basins located farther west closer to the overthrust belt twelve specific stratigraphic and sedimentologic criteria for the onset duration and termination of laramide deformation allow the chronology of basin development to be inferred independently for each basin maastrichtian initiation of laramide deformation was approximately synchronous throughout the laramide province but termination of laramide deformation was systematically diachronous from north to south between early and late eocene time widespread eocene erosion surfaces truncate syntectonic laramide sequences and are overlain by largely volcanic and volcaniclastic post laramide strata of eocene age in the north and oligocene age in the south fluvial depositional systems draining toward the great plains were dominant in perimeter and axial basins but ponded basins were occupied at times by large lakes that served as regional sediment traps paleocene drainages from ponded basins also led eastward toward the continental interior but partly interconnected lakes that developed within several ponded basins by mid eocene time were either closed hydrologically or else they drained westward into the tyee paleoriver of the pacific northwest

environmental impact of mineralised black shales abstract black shales are sedimentary rocks containing 0 5 of organic carbon they host polymetallic deposits which have been mined for cu ni zn mn p mo v u au and pge platinum group elements even sub economic occurrences provide potential risk of acid rock drainage when exposed to oxic surface environment the natural acid neutralisation potential varies depending on the adjacent rock units especially on the presence of calcareous rocks the chemical and mineralogical composition of black shale is reflected in the quality of the surface waters and groundwater cu ni pb u and zn are recognised as major pollutants though the environmental impact is characteristically polymetallic just like the black shale occurrences hence the environmental impacts have to be evaluated in each occurrence the proterozoic ni zn cu co deposit at talvivaara finland is reviewed in more detail as an example of a large low grade deposit that is currently exploited with open pit mining and a bioleaching process together with the proterozoic central african copperbelt the cambrian u mo deposits in sweden the cambrian ni mo pge deposits in china and the cambrian ordovician u deposits in south korea the devonian ni zn pge occurrences in yukon canada and kentucky usa and the permian cu ag deposits in poland and germany the mineralised horizons may be merely few centimetres thick like in yukon or hundreds of metres thick like at talvivaara both natural and anthropogenic environmental impacts of black shales are reviewed world wide and based on the overview of the state of the art an integrated research approach is suggested for the comprehensive assessment of the risk black shales are natural sources of soil and water contamination at talvivaara the geochemical background includes higher than average concentrations of ni cu zn and mn in glacial till peat surface waters and groundwater as well as in stream and lake sediments bioaccumulation by plants has been reported in china and korea even endemic diseases have been proposed to be linked with the contamination derived from the weathering and leaching of harmful elements from black shale anthropogenic actions exposing the black shale bedrock and associated soils to oxic conditions further intensifies acid rock drainage regional or nation wide mapping of the black shales is recommended to detect potential risk areas finland has recently completed the country wide mapping program of black shales with airborne geophysics integrated with geological petrophysical and geochemical studies the black shale database is actively used in regional planning and by environmental authorities research institutes and consulting companies in the case of the historical black shale mining areas like in the kupferschiefer in germany restoration measures have been applied to prevent further acid mine drainage in active and future mining projects a comprehensive environmental impact assessment with effective monitoring programmes and closure plans play a crucial role in the prevention of acid mine drainage from the black shale associated deposits

late cretaceous early eocene laramide uplift exhumation and basin subsidence in wyoming crustal responses to flat slab subduction low angle subduction of the farallon oceanic plate during the late cretaceous early eocene is generally considered as the main driver forming the high rocky mountains in wyoming and nearby areas how the deformation was transferred from mantle to upper crust over the great duration of deformation 40 myr is still debated here we reconstruct basin subsidence and compile paleoelevation thermochronology and provenance data to assess the timing magnitude and rates of rock uplift during the laramide deformation we reconstruct rock uplift as the sum of surface uplift and erosion constrained by combining paleoelevation and exhumation with regional stratigraphic thickness and chronostratigraphic information the amount and rate of rock uplift of individual laramide ranges was less than 2 4 4 8 km 0 21 0 32 mm yr during the early maastrichtian paleocene stage 1 and increased to more than 3 km 0 38 0 60 mm yr during the late paleocene early eocene stage 2 our quantitative constraints reveal a two stage development of the laramide deformation in wyoming and an increase of rock uplift during stage 2 associated with enhanced intermontane basin subsidence exhumation and uplift during stage 1 is consistent with eastward migration of cordilleran deformation associated with low angle subduction whereas the change in exhumation during stage 2 seems to follow a southwestward trend which requires an alternative explanation we here suggest that the increase of rock uplift rate during the late paleocene early eocene and the southwestward younging trend of uplift may be a response to the rollback and associated retreating delamination of the farallon oceanic slab

modeling the thermal hydrologic processes in a large scale underground heater test in partially saturated fractured tuff the drift scale test dst is being conducted in an underground facility at yucca mountain nevada to probe the coupled thermal hydrological mechanical and chemical processes likely to occur in the fractured rock mass around a potential high level nuclear waste repository thermal hydrological processes in the dst have been simulated using a three dimensional numerical model the model incorporates the realistic test configuration and all available site specific measurements pertaining to the thermal and hydrological properties of the unsaturated fractured tuff of the test block the modeled predictions were compared to the extensive set of measured data collected in the first year of this 8 year long test the mean error between the predictions and measurement at 12 months of heating for over 1600 temperature sensors is about 2 degrees c heat pipe signature in the temperature data indicating two phase regions of liquid vapor counterflow is seen in both the measurements and simulated results the redistribution of moisture content in the rock mass resulting from vaporization and condensation was probed by periodic air injection testing and geophysical measurements good agreement also occurred between the model predictions and these measurements the general agreement between predictions from the numerical simulations and the measurements of the thermal test indicates that ourmore fundamental understanding of the coupled thermal hydrologic processes at yucca mountain is sound however effects of spatial heterogeneity from discrete fractures that are observed in the temperature data are not matched by simulations from the numerical model which treat the densely spaced fractures as a continuum less

paleogeographic record of eocene farallon slab rollback beneath western north america eocene terrestrial strata in western north america are now dated with sufficient precision to examine the hypothesis that rollback of the farallon flat slab created a trenchward migrating wave of dynamic and thermal topography we use patterns of accumulation and unconformity lake type stratigraphy and physical and isotopic provenance tools to track its migration across the laramide foreland between 53 ma and 47 ma hydrologic ponding and coincident unconformity development began at 53 ma culminating at 51 8 ma in the hydrologic closure of an 900 000 km2 area between the cordilleran and rocky mountain divides four subsequent stream diversions and a southwest expanding regional unconformity record trenchward migration of uplift from 50 to 47 ma volcaniclastic detritus from magmatic centers coincident with the uplifted region progressively filled the green river formation lakes from north to south these findings are consistent with recent numerical and conceptual models of slab rollback that predict initial dynamic subsidence above the slab hinge followed by uplift and volcanism triggered by influx of asthenosphere beneath the overriding plate based on the surface record rollback proceeded systematically at a rate of 6 cm yr across the wyoming craton from 53 to 47 ma resulting in removal of the entire shatsky conjugate oceanic plateau from the base of the north american lithosphere

hit and run collision model for the laramide orogeny western united states the formation of the rocky mountains an event referred to as the laramide orogeny has presented a dilemma since the introduction of plate tectonics in scale and tectonic style the late cretaceous early tertiary orogeny resembles collisional orogenies such as the himalayas however no collider remains adjacent to the continental margin at the latitude of laramide features i e california to washington terranes of western british columbia and southeast alaska known together as baja bc may constitute the colliding plate geologic studies and paleomagnetic data suggest that baja bc collided with north america at the latitude of modern baja california the hit and was subsequently translated northward during oblique convergence the run to its present latitude between 94 ma and ca 40 ma northward translation of baja bc is spatially and temporally coincident with the ca 80 to 45 ma laramide orogeny suggesting a causal link between the events

subduction dynamics and the origin of andean orogeny and the bolivian orocline the building of the andes results from the subduction of the oceanic nazca plate underneath the south american continent however how and why the andes and their curvature the bolivian orocline formed in the cenozoic era 65 5 million years myr ago to present despite subduction continuing since the mesozoic era 251 0 65 5 myr ago is still unknown three dimensional numerical subduction models demonstrate that variations in slab thickness arising from the nazca plate s age at the trench produce a cordilleran morphology consistent with that observed the age dependent sinking of the slab in the mantle drives traction towards the trench at the base of the upper plate causing it to thicken thus subducting older nazca plate below the central andes can explain the locally thickened crust and higher elevations here we demonstrate that resultant thickening of the south american plate modifies both shear force gradients and migration rates along the trench to produce a concave margin that matches the bolivian orocline additionally the varying forcing along the margin allows stress belts to form in the upper plate interior explaining the widening of the central andes and the different tectonic styles found on their margins the eastern and western cordilleras the rise of the central andes and orocline formation are directly related to the local increase of nazca plate age and an age distribution along the margin similar to that found today the onset of these conditions only occurred in the eocene epoch this may explain the enigmatic delay of the andean orogeny that is the formation of the modern andes

apatite fission track evidence for laramide and post laramide uplift and anomalous thermal regime at the beartooth overthrust montana wyoming the crystalline rocks of the beartooth overthrust in southwest montana and northwest wyoming were uplifted and thrust over the northwest margin of the bighorn basin during the laramide orogeny the timing and geometry of that event is well documented in the synorogenic paleocene and early eocene sedimentary rocks that were deposited ahead of the rising beartooth basement block and partially over ridden as the block advanced the absence of post laramide sedimentary rocks on the block and in the adjacent bighorn basin has however precluded the reconstruction of the post orogenic tectonothermal history of this region we report here the results of fission track analysis of apatite from the three components of the beartooth over thrust with the aim of reconstructing the laramide and post laramide tectono thermal history of the southeast margin of the beartooth mountains apatite fission track ages and corresponding horizontal confined track length distributions hctlds from precambrian basement rocks constituting the upper plate of the beartooth overthrust indicate that from 7 to 12 km of uplift of the red lodge corner of the beartooth block has occurred since early paleocene time this amount of uplift occurred in two stages with an intervening mid tertiary period of tectonic quiescence the latter was a period of either 1 oligocene and or miocene deposition or 2 tectonic quiescence uplift of 4 to 8 km occurred during the first phase of cooling which lasted from early paleocene time 61 ma to early eocene time 52 ma during the second phase which began in late miocene early pliocene time and continues to the present day about 4 km of uplift occurred our fission track data suggest that the thermal regime in rocks above the beartooth overthrust was relatively stable during tertiary time the maximum geothermal gradient permitted by model thermal histories generated from our observed fission track data during post laramide time is 17 c km this value is the same as that of the present day geothermal gradient measured in the amoco beartooth well and suggests that a low geothermal gradient prevailed throughout tertiary time apatite fission track ages and hctlds from jurassic and cretaceous sedimentary rocks beneath the beartooth overthrust indicate that these rocks have remained 10 20 c cooler than overlying rocks in the shear zone and the lowermost part of the upper plate since 61 ma an observation that is not consistent with the stratigraphic position of these rocks we interpret this temperature to be the result of a persistent thermal regime in which ground water circulating through the sedimentary rocks of the lower plate cooled them and insulated them from conductive heat transfer from hotter overlying rocks this ground water circulation may have been responsible for flushing hydrocarbons out of the rock column explored by the beartooth well shear zone rocks experienced a higher temperature during cenozoic time than did rocks of the upper and lower plates this condition was maintained by flow through the shear zone of ground water heated to higher temperatures at deeper levels along the thrust

dynamic subsidence and uplift of the colorado plateau we use inverse models of mantle convection to explore the vertical evolution of the colorado plateau by satisfying multiple constraints seismic tomography stratigraphy in the western united states and great plains and other structural and volcanic data adjacent to the plateau the model provides predictions on the continuous history of colorado plateau vertical motion since 100 ma with the arrival of the flat lying farallon slab dynamic subsidence swept from west to east over the plateau and reached a maximum ca 86 ma two stages of uplift followed the removal of the farallon slab below the plateau one in the latest cretaceous and the other in the eocene with a cumulative uplift of 1 2 km both the descent of the slab and buoyant upwellings raised the plateau to its current elevation during the oligocene a locally thick plateau lithosphere enhances the coupling to the upper mantle so that the plateau has a higher topography with sharp edges the models predict that the plateau tilted downward to the northeast before the oligocene caused by northeast trending subduction of the farallon slab and that this northeast tilting diminished and reversed to the southwest during the miocene in response to buoyant upwellings

pb pb dating of hydrocarbon migration into a bitumen bearing ore deposit north wales previous attempts at u pb dating of uraniferous bitumens have had limited significance because of radioelement migration pb pb dating which can be undertaken regardless of recent lead migration has been successfully applied to uraniferous solidified bitumen from the ty gwyn copper deposit north wales analyses of five bitumen samples with variable mixtures of radiogenic and common lead yield a sup 207 pb sup 206 pb age of 248 plus minus 21 ma early triassic this age is interpreted as the date of hydrocarbon migration into the deposit and is reasonably consistent with the timing of hydrocarbon generation calculated from the regional burial history the pb pb dating method could be applied to date uraniferous bitumens representing hydrocarbon migration in diverse geologic environments

tectonic palaeoenvironmental forcing of clay mineral assemblages in nonmarine settings the oligocene miocene as pontes basin spain two small alluvial lacustrine subbasins developed during the early restraining overstep stages of the oligocene miocene as pontes strike slip basin nw spain later the basin evolved into a restraining bend stage and an alluvial swamp dominated depositional framework developed the palaeobiological record demonstrates that the oligocene miocene palaeoclimate in nw spain was subtropical warm and humid to subhumid the metamorphic and igneous basin catchment yielded clay assemblages made up by kaolinite illite and al smectite illite occurred as an original mineral in the source rock area whereas kaolinite and al smectite resulted mainly from weathering of feldspar and clinochlore respectively this detrital primary clay assemblage remained preserved in the colluvial alluvial fan and shallow lacustrine facies whose early diagenesis was influenced by diluted poorly evolved pore waters with neutral to slightly alkaline ph the original clay assemblage was mildly to strongly transformed under early diagenetic conditions in the lacustrine and swampy environments where significant hydrochemical and eh ph changes took place a fibrous magnesium rich clay mineral dominated assemblage palygorskite and sepiolite formed in shallow saline lakes and palustrine zones under the influence of magnesium rich alkaline waters moreover kaoliniteenriched assemblages formed in deep lacustrine swamp and swamp related alluvial zones under the influence of slightly to highly acidic pore waters pore water acidic conditions characterising environments with organic matter accumulation led to early diagenetic transformation of al smectite into kaolinite this process was relatively limited in some environments such as organic matter rich bottoms in meromictic lacustrine zones whereas it was pervasive in peat forming swamp zones the stratigraphic relationships between the diverse clay mineral assemblages in the as pontes basin fill demonstrate the coeval development of rather diverse clay compositions this clearly reflects the influence on clay assemblages of palaeoenvironmental changes forced by the morphological and tectonic evolution of the catchment basin system the interplay between climate and tectonic processes in the source areas did not result in major variations of the clay minerals fed into the basin conversely this tectonic sedimentation interplay influenced the evolution of the drainage and the water balance in the depositional zones causing a complex environmental hydrochemical evolution to occur as a consequence drastic early

elemental mobility in phosphatic shales during concretion growth and implications for provenance analysis shale normalized rare earth element ree patterns record variable redox conditions in coprolitic phosphorite concretions and their host shales from the pennsylvanian age cyclothems in the u s midwestern states of oklahoma kansas nebraska iowa and ohio as well as the mississippian age fayetteville shale of arkansas shale normalized enrichments in middle ree mree developed as the phosphatic concretions lithified under reducing conditions in pore waters of organic rich muds depletions in mree sm ho in host shales correspond to the mree enrichments in some nearby concretions rare and weak negative cerium depletions in both reworked and unreworked phosphorite concretions suggest exposure to oxygenated waters positive europium anomalies in thick phosphorite coatings on coprolitic phosphorite concretion cores suggest extreme reduction during lithification of the phosphorite coating flat ree patterns in both host shales and phosphorite concretions probably reflect detrital influence phosphate diagenesis can affect the trace element chemistry of black shale enough to alter provenance signals overall enrichment in ree in phosphorite relative to host shale suggests movement of ree as does the mree enriched phosphorite near the mree depleted host shale diagenetically mobile ree can affect la th sc relationships used in provenance analysis the extent of the diagenetic modification of la th sc distribution is related to the amount of p2o5 present typical la th sc distribution in host shale results when p2o5 values are below 0 5 high la abundance substantially skews la th sc distribution when p2o5 is above 5 0 but when p2o5 is between 0 5 and 5 0 the extent of the effect is unclear oxides of aluminum and other major elements may be useful in recording detrital influence and proximity to the shoreline in phosphorite concretions most of the concretions nearest to shoreline sources of detrital input have both flat ree patterns and elevated values of al2o3 al2o3 fe2o3

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

quantitative geochemical approach to pedogenesis importance of parent material reduction volumetric expansion and eolian influx in lateritization abstract using mass balance techniques we test the prevalent view that laterite genesis is dominated by in situ residual enrichment during chemical weathering of bedrock through calculation of net mass fluxes through the laterite soils in mali west africa we show that residual enrichment by removal of mobile elements with a corresponding increase in bulk porosity and decrease in bulk density contributes only a very minor fraction of the enrichment of al fe si and au instead we demonstrate that the abundance of these elements is due to the influx and accumulation by selective retention of chemically mature detritus of local and foreign origin clearly evident in micromorphological infilling features at the same sample depths that accumulation reaches extreme values we show that volumetric expansion in excess of 200 has occurred locally we infer that these spatially coincidental zones of mass influx of rock forming metals fe al si and also au with dilational hyperstrains result from a mutually reinforcing mechanical interaction between material influx and the effects of subsurface deformational processes such as shrink swell cycles and root growth and decay we propose that with progressive infilling of available connected voids by illuvial microsedimentary deposits of insoluble resistate and neoformed minerals the capacity for the combined skeleton and plasma to remain isovulumetric is exceeded we speculate that the resultant space problem is relieved by upwards expansion towards the overlying free surface continued translocation and void infilling occur and are limited to the depth where the size of translocational particles is smaller than that of the connected voids consequently progressive hyperstrains accumulate above this critical depth by the long term influence of a proposed translocational wedge of chemically resistant minerals against which numerous generations of plant roots have exerted stresses eclectic surficial contaminants involved are continuously derived from above leaving no indication of a relict source region within the present soil profile from which they might have been extracted instead the source region is largely the existing regolith column itself which releases local material and in addition is supplemented by deposition of colluvial detritus shed nearby by escarpment retreat

subduction zone evolution and low viscosity wedges and channels dehydration of subducting lithosphere likely transports fluid into the mantle wedge where the viscosity is decreased such a decrease in viscosity could form a low viscosity wedge lvw or a low viscosity channel lvc on top of the subducting slab using numerical models we investigate the influence of low viscosity wedges and channels on subduction zone structure slab dip changes substantially with the viscosity reduction within the lvws and lvcs for models with or without trench rollback overthickening of slabs is greatly reduced bylvws or lvcs two divergent evolutionary pathways have been found depending on the maximum depth extentofthelvwandwedgeviscosity assumingaviscositycontrastof0 1withbackgroundasthenosphere modelswithalvwthat extendsdown to 400km depthshow asteeply dipping slab while models with anlvw that extends to muchshallower depth such as 200 km can produce slabs that are flat lying beneath the overriding plate there is a narrow range of mantle viscosities that produces flatslabs 5to10 10 19 pas andthe slab flatteningprocessisenhanced bytrenchrollback slabcanbedecoupled fromthe overriding platewithalvcifthe thicknessisatleastafew10s ofkm the viscosityreduction isatleastafactor oftwoandthedepthextentofthe lvc is several hundred km these models have important implications for the geochemical and spatial evolution of volcanic arcs and the state of stress within the overriding plate the models explain the poor correlation between traditional geodynamic controls subductingplateageandconvergencerates onslabdip wepredictthatwhenvolcanicarcschangetheirdistancefromthetrench they could be preceded by changes in arc chemistry we predict that there could be a larger volatile input into the wedge when arcs migrate toward the trench and visa versa the transition of a subduction zone into the flat lying regime could be preceded by changes in the volatile budget such that the dehydration front moves to shallower depths our flat slab models shed some light on puzzling flat subductionsystems likeincentralmexico wherethereisnodeformationwithintheoverridingplateabovetheflatsegment thelack

isotopic evidence for preservation of cordilleran lithospheric mantle during the sevier laramide orogeny western united states it has been inferred that sevier laramide flat subduction imparted a large basal shear traction force to the overriding north american plate resulting in laramide rocky mountain foreland deformation and significant thinning of cordilleran lithosphere additional inferred consequences include regional refrigeration of cordilleran crust and suppression of synorogenic extensional collapse nd isotopic data from cenozoic mafic volcanic rocks indicate that normal thickness lithospheric mantle was preserved beneath the cordilleran craton from precambrian to late cenozoic time therefore cordilleran lithosphere was not thinned significantly and extensional collapse of orogenically thickened crust was not suppressed by refrigeration analogy with the south american cordillera suggests that flat subduction does not apply significant shear stress to the base of overriding plate lithosphere beyond the fore arc region and therefore does not mechanically thin overriding plate lithosphere except in the fore arc region the principal result of flat subduction was enhanced mechanical coupling between the underriding and overriding plates along the fore arc region this increased the horizontal end load due to relative plate convergence placed on the north american plate horizontal end load stress was transmitted laterally across both 1 a hinterland that had attained maximum crustal thickness and 2 the rigid colorado plateau into the laramide rocky mountain foreland early tertiary waning of plate convergence rates then allowed radial extensional collapse of the southern cordilleran region to drive the colorado plateau block northward resulting in late laramide rocky mountain foreland deformation

time of initial thrusting in the sevier orogenic belt idaho wyoming and utah reexamination of the distribution of fossils found in the earliest preserved synorogenic conglomerates within the sevier thrust belt suggests that initial thrust movement may be no older than aptian age this interpretation is corroborated by subsidence analyses of sedimentary sequences lying within and east of the idaho wyoming and utah thrust belts a major episode of middle cretaceous aptian cenomanian subsidence is interpreted as recording the initiation of thrust loading deformation in the adjacent sevier orogenic belt an earlier subsidence event took place during middle jurassic time more than 30 m y prior to the cretaceous event and may be the result of tectonic events to the west that are unrelated to thrust deformation in the idaho wyoming and utah thrust belts we find no verifiable evidence to support previous interpretations that sevier belt deformation and uplift began in late jurassic time

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

stable hydrogen and oxygen isotopes in mineral bound water and the indication for chemical weathering intensity abstract chemical weathering plays a key role in the long term climate change and global biogeochemical cycle in this study a 5 1 m long basalt developed weathering profile from hunan province china was selected for the analyses of major elements grain size ph total organic carbon thermogravimetric tg and differential thermogravimetric properties dtg as well as stable isotopes d and 18 o in mineral bound waters the major purpose is to distinguish different types of mineral bound water and to verify whether hydrogen and oxygen isotopes of mineral bound water can indicate chemical weathering intensity based on the tg and dtg results different types of mineral bound water were extracted by a sequential heating extraction technique 40 120 c 120 300 c 300 600 c and 600 900 c the mineral bound water lost below 120 c is absorbed water a mixture of interlayer and crystal waters occurs at 120 300 c and above 300 c is mostly constitution water hydrogen and oxygen isotopic ratios at top 2 m are subject to the influences of eolian and pedogenic processes the absorbed water has been exchanged and reached isotopic equilibrium with ambient soil water while the crystal water and interlayer water cannot be separated by heating method in this study hydrogen and oxygen isotopes of constitution water can indicate chemical weathering showing positive relationships with weathering intensity although the mechanism for their indication to chemical weathering remains further investigation we suggest that the isotopic fractionation between the formation of clay minerals and surface water should be taken into account this research sheds new light on mineral bound water phase and a potential proxy for tracing the process of chemical weathering

rhenium and osmium isotopes in black shales and ni mo pge rich sulfide layers yukon territory canada and hunan and guizhou provinces china rhenium and osmium abundances and osmium isotopic compositions were determined by negative thermal ionization mass spectrometry for samples of devonian black shale and an associated ni enriched sulfide layer from the yukon territory canada the same composition information was also obtained for samples of early cambrian ni mo rich sulfide layers hosted in black shale in guizhou and hunan provinces china this study was undertaken to constrain the origin of the pge enrichment in the sulfide layers samples of the ni sulfide layer from the yukon territory are highly enriched in re os and other pge with distinctly higher re 192os but similar pt re compared to the black shale host re os isotopic data of the black shale and the sulfide layer are approximately isochronous and the data plot close to reference isochrons which bracket the depositional age of the enclosing shales samples of the chinese sulfide layers are also highly enriched in re os and the other pge re 192os are lower than in the yukon sulfide layer re os isotopic data for the sulfide layers lie near a reference isochron with an age of 560 ma similar to the depositional age of the black shale host the osmium isotopic data suggest that re and pge enrichment of the brecciated sulfide layers in both the yukon territory and in southern china may have occurred near the time of sediment deposition or during early diagenesis during the middle to late devonian and early cambrian respectively

mineralogical and geochemical constraints on environmental impacts from waste rock at taojiang mn ore deposit central hunan china the mineralogy and geochemistry of the waste rocks distributed at taojiang mn ore deposit central hunan province china were studied using x ray powder diffraction xrd electron microprobe analysis empa fitted with energy dispersive spectrometer eds and inductively coupled plasma mass spectrum atomic emission spectra icp ms aes with the aim of predicting the environmental impacts of weathering of the waste rocks the mineralogical results from microscope observation and xrd and empa studies show that the waste rock is composed of black shale and minor mn carbonates the oxidation of sulfide minerals such as galena pyrite and chalcopyrite is accompanied by decomposition of mn carbonates and k feldspar during exposure to atmospheric o2 the geochemical characteristics of major rare earth elements ree and trace elements of the waste rocks also show that the waste rock can be divided into black shale and mn carbonate and both of them are currently under chemical weathering the major alkalies and alkaline elements ca mg na k rb sr and cs and major elements fe s and p and heavy metals sc v cr th u sn co ni cu zn pb mo cd sb an tl are being released during weathering the mobility of alkalis and alkaline elements ca mg na k rb sr and cs is controlled by decomposition of mn carbonates the dispersion of cr sc and th u might be related to weathering of k feldspar and the release of the heavy metals co ni cu zn pb mo cd sb and tl is dominated by the breaking of sulfide minerals the ree of the waste rocks and surrounding soils and the spidery distribution patterns of heavy metals in the waste rocks the surrounding soils and the surface waters show that weathering of the waste rocks and bedrock might be the sources of heavy metal contamination for the surrounding soils and surface water system for the mining area this is predicted by the mass balance calculation by using zr as an immobile element therefore it is urgently necessary take measures to treat the waste rocks distributed throughout the area for the local environmental protection

the development of middle rare earth element enrichments in freshwaters weathering of phosphate minerals abstract many phosphatic minerals of biogenic authigenic and diagenetic origin are distinguished by rare earth element ree compositions which have a well developed middle rare earth element mree enrichment defined by a gradual increase in the shale normalized ratios of ree toward the middle of the ree series la to lu also the ree composition of dissolved matter in the waters of the amazon fly and sepik rivers as well as other river lake and ground waters have well developed mree enrichments the development of mree enrichments was studied through a series of leaching experiments using river bank sediments from the amazon fly sepik and mississippi rivers a well characterized phosphate mineral rich shale with a pronounced mree enrichment in its bulk composition was also leached in order to better assess the relationship between the weathering of phosphate minerals and the formation of mree enriched solutions the two leaching solutions per sediment consisted of filtered lake water at ph 5 and the same water adjusted to ph 2 leaching experiments with the four river sediments result in extensive fractionation whereby the ree compositions of the solutions develop mree enrichments from starting sediments that show no mree enrichments the ph 2 leachates have much higher concentrations of the ree and more fully developed mree enrichments than do the ph 5 leachates the mree enrichments at ph 2 usually form within an hour of starting the experiments the phosphatic shale results show that there is preferential release of large amounts of mree at ph 5 as well as at ph 2 demonstrating the weather ability of the phosphatic minerals at phs of natural freshwaters the sepik river ph 5 experiment also shows significant mree enrichment under near neutral conditions the development and retention of the mree enrichments in the leaching solutions is accompanied by an increase in dissolved phosphate concentrations although the magnitudes of the mree enrichment do not directly correlate with the percent of phosphate released the experimental data suggest that the preferential dissolution of phosphatic minerals during weathering can result in extensive ree fractionation between bulk river sediment and water leading to freshwaters with mree enrichments

statistical empirical index of chemical weathering in igneous rocks a new tool for evaluating the degree of weathering abstract chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering however the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock to overcome this limitation the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis pca of a large dataset derived from unweathered igneous rocks and their weathering profiles the pca analysis yields two principal components pc1 and pc2 which capture 39 23 and 35 17 of total variability respectively the extent of weathering is reflected by variation along pc1 primarily due to the loss of na 2 o and cao during weathering in contrast pc2 is the direction along which the projections of unweathered felsic intermediate and mafic igneous rocks appear to be best discriminated therefore pc1 and pc2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock subsequently pc1 and pc2 were then mapped onto a ternary diagram mfw diagram the m and f vertices characterize mafic and felsic rock source respectively while the w vertex identifies the degree of weathering of these sources independent of the chemistry of the unweathered parent rock the w index has a number of significant properties that are not found in conventional weathering indices first the w index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides whereas most conventional indices are defined by between two and four oxides second the w index provides robust results even for highly weathered sesquioxide rich samples third the w index is applicable to a wide range of felsic intermediate and mafic igneous rock types finally the mfw diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock

post paleozoic alluvial gravel transport as evidence of continental tilting in the u s cordillera the western united states contains three thin but remarkably widespread alluvial conglomeratic units that record episodes of large scale tilting across the u s cordilleran orogen in post paleozoic time these units are 1 the shinarump conglomerate of late triassic age exposed in northern arizona and adjacent parts of utah nevada and new mexico 2 lower cretaceous gravel deposits that overlie the morrison formation throughout the rocky mountain region and 3 the gravel rich parts of the miocene pliocene age ogallala group in western nebraska and adjacent southeastern wyoming paleoslopes of the rivers depositing these units were in the range of 10 24 to 10 23 based on paleohydraulic calculations however depositional thickness trends of these units are not sufficient to have generated such steep paleoslopes thus long wavelength tilting of the earth s surface must have occurred for these gravels to be transported although these units were deposited adjacent to large tectonic features including an evolving and migrating continental arc and for the ogallala group the northward propagating rio grande rift the tilting occurred over wavelengths too broad to be directly generated by these features these widespread gravel units attest to the interplay between the creation of subduction related isostatic and dynamic topography and continental sedimentation hence paleotopography as determined from calculated transport gradients of sedimentary deposits provides a

trace and rare earth element geochemistry of phosphate nodules from the lower cambrian black shale sequence in the mufu mountain of nanjing jiangsu province china abstract phosphate nodules are abundant in the lowermost section of the lower cambrian black shale sequence along a ne trend belt in the yangtze platform south china in this study we examined the neoproterozoic cambrian mufu mountain section near nanjing of jiangsu province and conducted a detailed trace and rare earth element ree study on the phosphate nodules we employed a step leaching acid dissolution protocol of 1 m hac and 1 m hcl respectively to separate carbonate from phosphate mineral contributions in the nodules both the hac leached and hcl leached fractions of the phosphate nodules show similar symmetrical variations in trace and ree concentrations and ratios the total rees and a number of redox sensitive trace metals such as v cr mo ni abundances show a systematic increase from the core to rim whereas the u and mn abundances decrease from the core to rim in most of the nodules similar trends are also observed for the rb sr u th co ni and v ni ratios but these trends in the hac leached fractions are less pronounced than the hcl leached fractions all of the hcl leached fractions for the nodule cores show seawater like shale normalized ree patterns but the rims of the nodules display slightly mree enriched and hree depleted patterns we suggest that the phosphate nodules may have formed in a basinal setting beneath a stratified water column during early cambrian and the compositional variations of rees and redox sensitive trace elements from the core to rim may record a changing redox condition and fluid mixing during different stages of nodule growth the cores of the nodules preserve more pronounced negative ce anomalies and progressively hree enriched patterns which may retain primary early cambrian seawater chemistry whereas the nodule rims record chemistry consistent with changed redox conditions and or influences from pore fluids such as generated from degradation of organic matter

inherited landscapes and sea level change enabled by recently gained understanding of deep seated and surficial earth processes a convergence of views between geophysics and sedimentary geology has been quietly taking place over the past several decades surface topography resulting from lithospheric memory retained at various temporal and spatial scales has become the connective link between these two methodologically diverse geoscience disciplines ideas leading to the hypothesis of plate tectonics originated largely with an oceanic focus where dynamic and mostly horizontal movements of the crust could be envisioned but when these notions were applied to the landscapes of the supposedly rigid plate interiors there was less success in explaining the observed anomalies in terrestrial topography solid earth geophysics has now reached a developmental stage where vertical movements can be measured and modeled at meaningful scales and the deep seated structures can be imaged with increasing resolution concurrently there have been advances in quantifying mechanical properties of the lithosphere the solid outer skin of earth usually defined to include both the crust and the solid but elastic upper mantle above the asthenosphere the lithosphere acts as the intermediary that transfers the effects of mantle dynamics to the surface these developments have allowed us to better understand the previously puzzling topographic features of plate interiors and continental margins on the sedimentary geology side new quantitative modeling techniques and holistic approaches to integrating source to sink sedimentary systems have led to clearer understanding of basin evolution and sediment budgets that allow the reconstruction of missing sedimentary records and past geological landscapes

flexural versus dynamic processes of subsidence in the north american cordillera foreland basin 1 dynamic subsidence related to subduction is an important process in retroarc foreland basin systems dynamic subsidence in the north american retroarc foreland has been proposed as dominant in the late cretaceous however questions remain about the nature of the subcrustal load and the basin response to such processes we present new isopach data using 130 data points covering a large portion of the u s and a revised flexural analysis of the sevier foreland higher rigidity associated with the wyoming craton can best model flexural subsidence directly prior to 81 ma we constrain the transition from flexural to nonflexural subsidence to 81 ma and correlate this with large late cretaceous progradation the locus of subsidence and the location of the subducted shatsky oceanic plateau suggest that dynamic loading from viscous flow above the subducting plate is the mechanism driving dynamic subsidence in the retroarc foreland basin of the north american cordillera

the role of oceanic plateau subduction in the laramide orogeny the cause of the laramide phase of mountain building remains uncertain conceptual models implicate the subduction of either ocean ridges or conjugates of the buoyant hess or shatsky oceanic plateaux independent verification of these models has remained elusive because the putative ridges or plateaux are no longer at the earth s surface inverse convection models have identified two prominent seismic anomalies on the recovered farallon plate here we combine inverse convection models with reconstructions of plate motions to show that these seismic anomalies coincide palaeogeographically with the restored positions of the shatsky and hess conjugate plateaux as they subducted beneath north america specifically the distribution of laramide crustal shortening events tracked the passage of the shatsky conjugate beneath north america whereas the effects of the hess conjugate subduction were restricted to the northern mexico foreland belt we propose that continued subduction caused the oceanic crust to undergo the basalt eclogite phase transformation during which the shatsky conjugate lost its extra buoyancy and was effectively removed increases in slab density and coupling between the overriding and subducting plates initially dragged the surface downward followed by regional scale surface rebound we conclude that laramide uplift resulted from the removal rather than emplacement of the shatsky conjugate

metal dispersion in groundwater in an area with natural and processed black shale nationwide perspective and comparison with acid sulfate soils black shale is often rich in sulfides and trace elements and is thus a potential environmental threat in a manner similar to acid sulfate soils and active or abandoned sulfide mines this study aims at characterising how exposed and processed mined and burnt black shale alum shale in degerhamn se sweden affects the chemistry al as ba cd ca cr co cu fe pb mg mn mo ni k si na sr s u v and zn of the groundwater there were large variations in groundwater chemistry between nearby sampling points while the temporal variations generally were small acidic groundwater around ph 4 found in deposits of burnt and carbonate poor shale where the conditions for sulfide oxidation were favourable was strongly elevated in al u and several chalcophilic metals cd co cu ni and zn cadmium and u were also together with mo abundant in many of the near neutral waters both in the non mined black shale bedrock and in the deposits of burnt shale an extrapolation to a national level suggests that the dispersion of ni from naturally occurring black shale is similar to that from anthropogenic point sources while for cd and as it is assessed to be approximately one tenth of that from point sources the processed shale was however a much larger source of metals than the black shale bedrock itself showing this material s potential as a massive supplier of metals to the aquatic environment a comparison of waters in contact with the processed cambrian ordovician black shale in degerhamn and acid sulfate soils of the region shows that these two sulfide bearing materials in many respects very different delivers basically the same suite of trace elements to the aquatic environment this has implications for environmental planning and protection in areas where these types of materials exist

lead and strontium isotopes as monitors of experimental granitoid mineral dissolution abstract flow through dissolution experiments were carried out on crushed granitoid rock the elat granite and three mineral separates plagioclase perthite and biotite chlorite from this rock at ph 1 and 25 c major element concentrations were combined with pb and sr isotopic analyses of starting materials and output solutions and together enabled us to elucidate several important mechanisms related to granitoid rock weathering we observed an initial stage of rock dissolution

dynamic uplift during slab flattening subduction exerts a strong control on surface topography and is the main cause of large vertical motions in continents including past events of large scale marine flooding and tilting the mechanism is dynamic deflection the sinking of dense subducted lithosphere gives rise to stresses that directly pull down the surface here we show that subduction does not always lead to downward deflections of the earth s surface subduction of young lithosphere at shallow angles flat subduction leaves it neutrally or even positively buoyant with respect to underlying mantle because the lithosphere is relatively warm compared with older lithosphere and because the thickened and hence drier oceanic crust does not undergo the transformation of basalt to denser eclogite accounting for neutrally buoyant flat segments along with large variations in slab morphology in the south american subduction zone explains along strike and temporal changes in dynamic topography observed in the geologic record since the beginning of the cenozoic our results show that the transition from normal subduction to slab flattening generates dynamic uplift preventing back arc marine flooding