detecting hydrologic deformation using grace and gps 1 hydrological processes cause variations in gravitational potential and surface deformations both of which are detectable using space geodetic techniques we computed elastic deformation using continental water load estimates derived from the gravity recovery and climate experiment and compared to 3d deformation estimated from gps observations the agreement is very good in areas where large hydrologic signals occur over broad spatial scales with correlation in horizontal components as high as 0 9 agreement is also observed at smaller scales including across europe this suggests that a both techniques are perhaps more accurate than previously thought and b a large percentage of the non linear variations seen in our gps time series are most likely related to geophysical processes rather than analysis error low correlation at some sites suggests that local processes or site specific analysis errors dominate the gps deformation estimates rather than the broad scale hydrologic signals detected by grace

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

observing coseismic gravity change from the japan tohoku oki 2011 earthquake with goce gravity gradiometry the japan tohoku oki earthquake 9 0 mw of 11 march 2011 has left signatures in the earth s gravity field that are detectable by data of the gravity field recovery and climate experiment grace mission because the european space agency s esa satellite gravity mission gravity field and steady state ocean circulation explorer goce launched in 2009 aims at high spatial resolution its measurements could complement the grace information on coseismic gravity changes although time variable gravity was not foreseen as goal of the goce mission we modeled the coseismic earthquake geoid signal and converted this signal to vertical gravity gradients at goce satellite altitude we combined the single gradient observations in a novel way reducing the noise level required to detect the coseismic gravity change subtracted a global gravity model and applied tailored outlier detection to the resulting gradient residuals furthermore the measured gradients were along track filtered using different gradient bandwidths where in the space domain gaussian smoothing has been applied one year periods before and after earthquake occurrence have been compared with the modeled gradients the comparison reveals that the earthquake signal is well above the accuracy of the vertical gravity gradients at orbital height moreover the obtained signal from goce shows a 1 3 times higher amplitude compared with the modeled signal besides the statistical significance of the obtained signal it has a high spatial correlation of 0 7 with the forward modeled signal we conclude therefore that the coseismic gravity change of the japan tohoku oki earthquake left a statistically significant signal in the goce measured gravity gradients

calcic paleosols their use in subsurface stratigraphy analysis of well log data from cenozoic basin fill of the deer lodge valley southwestern montana provides evidence for identifying paleosols and paleosol stacks in the subsurface the paleosol stacks are continental sequence boundary markers and appear as several relatively thin high velocity high density zones within basin fill zone thickness ranges from 1 to 1 5 m zones are stacked to thicknesses of up to 15 m density varies within the zones by as much as 0 6 g cm3 and differs by as much as 0 9 g cm3 from material immediately above these zones velocity differs by as much as 10 ft ms from the overlying material and causes bright reflections on seismic sections synthetic seismograms are used to tie well log and seismic data basing our interpretation upon well log data and well cuttings analyses we determined the high velocity high density zones to be limestone the pedogenic origin of the limestone is shown by 1 well cutting chips from the high velocity high density zones that exhibit pedogenic features associated with calcic paleosols 2 paleosol horizonation interpreted from well log analysis 3 the absence of minerals normally associated with lacustrine deposits and 4 comparison with surface paleosol exposures

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

kinematics and timing of three superposed extensional systems east central idaho evidence for an eocene tectonic transition cenozoic crustal extension in east central idaho began about 50 ma and continues at present three distinct episodes characterize one of the longest intervals of cenozoic extension yet documented in the north america cordillera crosscutting relationships between ne striking normal faults and volcanic rocks regional dike trends and slickenline data indicate nw se extension during peak eocene volcanism about 49 48 ma episode 1 ne striking normal faults with at most a few kilometers of offset formed in an intraarc setting during rapid ne subduction of oceanic plates under the pacific northwest north to nnw striking and west dipping normal faults with offsets up to 10 15 km formed during a younger middle eocene to oligocene basin forming event episode 2 this newly documented episode was the most important extensional event in east central idaho and began during the waning phases of challis volcanism wsw ene to sw ne extension during episode 2 was nearly perpendicular to the extension direction during episode 1 and perpendicular to the grain of the idaho montana fold and thrust belt the flip in extension direction between episode 1 and episode 2 is tightly constrained by 40ar 39ar age determinations to have taken place at the end of eocene challis magmatism about 46 48 ma i infer that plate boundary forces controlled the geometry of normal faults and dikes during episode 1 whereas internal stresses within previously thickened crust drove major sw to wsw directed extension during episode 2 a drop in convergence rates between the north american and farallon plates between 59 ma and 42 ma stock and molnar 1988 may coincide with the onset of gravitational spreading during episode 2 and may also explain the abrupt end of eocene magmatism in the pacific northwest miocene and younger sw dipping basin and range faults episode 3 extended the region in a ne sw direction although faults formed during episode 2 and episode 3 are not parallel slickenlines indicate only small changes in slip vector trends suggesting little rotation of the extension direction in east central idaho since 46 ma

stratigraphic record of the yellowstone hotspot track neogene sixmile creek formation grabens southwest montana abstract the sixmile creek formation fills deep grabens in southwest montana and preserves a stratigraphic record of the evolution of the yellowstone hotspot track from 17 ma to 2 ma the ruby beaverhead big hole deer lodge medicine lodge grasshopper three forks canyon ferry jefferson melrose wise river and paradise grabens were active during outbreak of the hotspot they appear to be parts of a radial system of extensional structures that may have formed on a broad dome that was centered on the hotspot outbreak area in southwest idaho and southeast oregon early in the evolution of the grabens massive debris flows surged down paleogene paleovalleys from uplifted and tilted horst blocks and accumulated in the grabens the grabens captured runoff from the hotspot dome with thick deposits of river gravel that appear to have been derived in part from east central idaho as the hotspot track propagated along the eastern snake river plain silicic ash fell into the graben drainage basins and was reworked into thick fluvial beds along graben axes the grabens were cross cut by northwest trending late neogene grabens that propagated on the flanks of silicic volcanic centers along the hotspot track the late neogene grabens diverted the middle miocene drainage patterns in southwest montana

high resolution isotopic record of c4 photosynthesis in a miocene grassland abstract the origin and spread of grasslands is one of the key evolutionary events in the cenozoic which is characterized by long term cooling and drying climatic conditions one way to examine the relationship between vegetation and climate is to study the isotopic composition of organic carbon preserved in paleosols paleosols that preserve organic matter in the form of carbonaceous root traces provide direct evidence of the proportion of c3 to c4 biomass that grew in the soil in contrast with pedogenic carbonate 13c values which may also reflect complicating factors including mixing from atmospheric 13c in low productivity ecosystems a high temporal and spatial resolution reconstruction of past ecosystems was derived from thirty five paleosols in a thirty four meter section of the sixmile creek formation at timber hills montana usa that was deposited during the miocene 10 2 8 9 ma ago phytoliths were extracted from paleosol samples to compare vegetation assemblages to inferences based on isotopic compositions with both proxies giving similar results isotopic results from organic matter indicate both a small component of c4 photosynthetic plants locally prior to their regional expansion to dominance in the late miocene through the early pleistocene and large variation in the abundance of c4 plants 0 25 in this ecosystem both laterally and on a 100 kyr timescale in contrast pedogenic carbonate 13c values from this site indicate a high proportion of c4 photosynthesis that is at odds with both phytolith and 13corg results suggesting that the carbonate values are biased by diagenesis or diffusion of atmospheric co2 and that a similar issue may impact previous paleovegetation reconstructions based on pedogenic carbonates quantitative reconstructions of mean annual temperature and mean annual precipitation indicate little local variability through time and that the fluctuations in c4 proportion were not climatically driven instead the variable proportion of c4 photosynthesis is best explained by ecosystem scale variables such as succession fluvial avulsion and fire regime

improved methods for observing earth s time variable mass distribution with grace using spherical cap mascons we discuss several classes of improvements to gravity solutions from the gravity recovery and climate experiment grace mission these include both improvements in background geophysical models and orbital parameterization leading to the unconstrained spherical harmonic solution jpl rl05 and an alternate jpl rl05m mass concentration mascon solution benefitting from those same improvements but derived in surface spherical cap mascons the mascon basis functions allow for convenient application of a priori information derived from near global geophysical models to prevent striping in the solutions the resulting mass flux solutions are shown to suffer less from leakage errors than harmonic solutions and do not necessitate empirical filters to remove north south stripes lowering the dependence on using scale factors the global mean scale factor decreases by 0 17 to gain accurate mass estimates ocean bottom pressure obp time series derived from the mascon solutions are shown to have greater correlation with in situ data than do spherical harmonic solutions increase in correlation coefficient of 0 08 globally particularly in low latitude regions with small signal power increase in correlation coefficient of 0 35 regionally in addition to reducing the error rms with respect to the in situ data reduction of 0 37 cm globally and as much as 1 cm regionally greenland and antarctica mass balance estimates derived from the mascon solutions agree within formal uncertainties with previously published results computing basin averages for hydrology applications shows general agreement between harmonic and mascon solutions for large basins however mascon solutions typically have greater resolution for smaller spatial regions in particular when studying secular signals

protolith age of the swakane gneiss north cascades washington evidence of rapid underthrusting of sediments beneath an arc 1 the metamorphic core of the north cascades largely comprises island arc and oceanic terranes juxtaposed prior to circa 96 ma magmatism however the tectonic affinity of the structurally deepest terrane the 9 12 kbar swakane gneiss is distinctly different from other terranes in the core it is not intruded by arc related plutons and contains abundant precambrian zircons new u pb analyses of detrital zircons from the swakane gneiss yield dates from 73 ma to 1610 ma with a dominant late cretaceous population these data indicate that the swakane protolith was deposited as late as 72 5 0 6 ma the 206pb 238u date of the youngest detrital grain following deposition the gneiss was intruded by peraluminous leucogranite sheets that may represent partial melt derived from the gneiss at near to postpeak p t conditions one sheet yielded a u pb crystallization age of 68 36 0 07 ma which indicates that the gneiss was deeply buried within 5 myr of deposition two possible mechanisms considered for this rapid burial 7 mm yr are overthrusting of a forearc or back arc basin by older crystalline rock or underthrusting of trench sediments during low angle subduction the model involving overthrusting of a forearc or back arc basin is most consistent with thermobarometric and isotopic data and the regional geologic setting of the cascades core rapid burial of the swakane protolith is coincident with burial of sediments that formed the pelona orocopia and rand schists of southern california however differences in peak metamorphic temperatures indicate that conditions of burial must have varied along the plate margin

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

a conceptual tectonostratigraphic model for seismic facies migrations in a fluvio lacustrine extensional basin one of the most fundamental differences between lacustrine basins and many marine basins is the stratigraphic response to differential tectonic subsidence because the water volume of a lake is finite tilting of the valley floor redistributes the lake water if the lake water level is below a hinge point fulcrum that experiences no net subsidence the lake shoreline is translated toward the site of subsidence and a deeper lake forms this tectonostratigraphic model for rift lake sedimentation is tested in a seismic and sequence stratigraphic study of deltaic and lacustrine deposits that accumulated in a cenozoic extensional basin beneath goshute valley nevada seismic sequences exhibit an internal cyclic stacking hierarchy of seismic reflections interpreted as the stratigraphic response of a lowstand paleolake to tectonism forced regression and subsequent lake level restoration transgressive and highstand systems tracts

paleogene postcompressional intermontane basin evolution along the frontal cordilleran fold and thrust belt of southwestern montana the paleogene renova formation is the earliest record of postcompressional sedimentation within and adjacent to the helena salient of the cordilleran fold and thrust belt in southwestern montana paleocurrent and compositional data from basin margin facies document radiating paleodispersal away from high relief 2 km highlands coincident with modern mountainous areas source rocks within the paleohighlands included the same archean metamorphic proterozoic paleozoic and mesozoic sedimentary and mesozoic plutonic and vo l canic rocks as exposed in modern uplifts paleocurrent and compositional data from trunk fluvial conglomerates and sandstones document the existence of an interbasinal drainage system that connected the three forks western gallatin and townsend basins with headwaters farther to the west and southwest near the present day montana idaho border overall the distribution of paleogene mountainous areas and basins closely resembled modern geography and the paleogene drainage network was strikingly similar to the modern missouri river headwater system the renova formation records the early stages of decay of the cordilleran orogenic belt including the evolution of a complex intermontane basin network in southwestern montana high energy late cretaceous to early eocene fluvial systems carved deep large scale paleovalleys into the orogenic wedge along zones of structural and stratigraphic weakness at least a 5 km thickness of overburden was removed during this time incision was temporally correlative with early cenozoic regional uplift and subtropical climatic conditions subsequent deposition of the renova formation was temporally correlative with the cessation of uplift the initiation of crustal extension and climatic cooling however extension is not interpreted to have played a major role in earliest basin development

regional scale variability in the spread of grasslands in the late miocene abstract a new paleovegetation reconstruction based on both phytolith and paleosol carbon isotopic data is presented for the middle late miocene 11 2 9 5 ma of southwestern montana both sources of data indicate an open habitat c3 grassland ecosystem with a small c4 component

cenozoic paleoclimate on land in north america abstract paleotemperature and paleoprecipitation over the past 40 m yr can be inferred from the degree of chemical weathering and depth of carbonate nodules in paleosols of oregon montana and nebraska paleosol records show that late eocene 35 ma middle miocene 16 ma late miocene 7 ma and early pliocene 4 ma warm climatic episodes were also times of a wet climate in oregon montana and nebraska oregon and nebraska were humid during warm wet times but montana was no wetter than subhumid within the rain shadow of intermontane basins global warm wet paleoclimatic spikes steepened rather than flattened geographic gradients of rocky mountain rain shadows long lived mountain barriers created dusty dry basins with sedimentation rates high enough to preserve milankovitch scale 100 41 kyr global paleoclimatic variation in some sequences of paleosols greenhouse warm wet climates indicated by paleosols were also peaks of diversity for north american plants and animals and coincided with advance

sequence stratigraphy of cenozoic continental rocks southwestern montana because the presently used bozeman group lithostratigraphy is difficult to apply to cenozoic basin fill rocks in the jefferson beaverhead melrose and divide valleys southwestern montana we advocate the use of sequence stratigraphy surface sequence boundaries are in many cases marked by calcic paleosol zones these zones can be projected into the subsurface and tied to seismic reflection data density velocity contrasts between calcic paleosol zones and overlying nonpedogenic rocks generate bright reflectors that define sequence boundaries sequence boundary delineation is further enhanced by reflection termination patterns similar to those found in marine strata sequence age calibration is based upon vertebrate fossil and radiometric age data five sequences separated by basin wide unconformities are recognized most sequence bounding unconformities are marked by paleosols an occurrence not previously reported for cenozoic strata of southwestern montana the sequences and their age ranges are 1 bridgerian uintan approximately 50 to 44 ma calc alkaline volcanic flows and interstratified sedimentary rocks 2 duchesnian to whitneyan approximately 42 to 30 ma terrestrial sedimentary and volcanic rocks 3 arikareean approximately 27 to 21 ma terrestrial sedimentary and volcanic rocks 4 barstovian to blancan approximately 16 to 4 ma terrestrial sedimentary and volcanic rocks and 5 early quaternary approximately 1 8 ma to holocene terrestrial sedimentary and volcanic rocks

onshore to offshore anatomy of a late quaternary source to sink system po plain adriatic sea italy abstract in understanding the evolution of siliciclastic systems late quaternary analogs may enable reliable predictive models of facies tract architecture the po plain adriatic sea system where a wealth of research has been conducted during the last 20 years represents one of the most intensively investigated late quaternary successions with the aid of a chronologically well constrained stratigraphy paleoenvironmental evolution is tracked for the first time from fluvial to deep marine realms over 1000 km in length vertical stacking trends onshore and stratal terminations offshore are the key observations that allow identification of surfaces with sequence stratigraphic significance systems tract boundaries in the distinct segments of the system recurring motifs in stratigraphic architecture showing tight coupling of sedimentary responses among source area catchment basin and coastal and marine depocenters reveal a cyclicity driven by glacio eustatic fluctuations in the milankovitch band due to high rates of subsidence middle pleistocene forced regressive systems tracts are exceptionally expanded and the mis5e mis2 interval late pleistocene preserves a nearly continuous record of fourth order 100 kyr stepwise sea level fall the stratigraphic architecture of last glacial maximum deposits highlights the genetic relations between channel belt development pedogenesis and sediment delivery to the lowstand delta through narrow incised valley conduits the late glacial holocene succession records the last episode of sea level rise and stabilization through well developed patterns of shoreline transgression regression tst hst that can be readily traced updip from offshore to onshore locations architectural styles across the whole system reflect a dominance of allogenic forcing in the tst as opposed to a predominantly autogenic control on stratigraphic development in the hst external drivers of facies architecture were also effective on millennial timescales the younger dryas cold reversal which marks the transgressive surface on land records a short lived episode of subaqueous progradation that is correlative onshore with widespread immature paleosol development and small sized channel belt formation quantitative assessment of sediment budgets over different time intervals requires precise positioning of the key bounding surfaces based on this approach we outline for the first time over the entire po adriatic basin an estimate of the sediment volumes stored in each systems tract

the significance of incision and fluvial sedimentation in the basal white river group eocene oligocene badlands of south dakota u s a abstract a newly defined lithostratigraphic unit the chamberlain pass formation cpf records the initial episode of incision fluvial sedimentation and pedogenesis in sw south dakota following the retreat of the cretaceous interior seaway the cpf is middle to late eocene in age and consists of fluvial sandstone and mudstone pedogenic modification of the unit has created a distinctive pedostratigraphic unit the interior paleosol series the cpf thickens from west to east achieving a maximum channel belt thickness of 11 m paleoflow data indicate that deposition of the cpf was restricted to a fault controlled basin southeast of the black hills uplift sandstones in the cpf were derived from a recycled sedimentary rock source area to the west in contrast sandstones in the overlying chadron formation late eocene had a variety of sources including the precambrian core rocks of the black hills uplift deposition of the cpf brackets four significant paleogene changes in baselevel that occurred in this region these events were 1 late cretaceous to middle eocene relative baselevel fall weathering and erosion of the cretaceous pierre shale to form the yellow mounds paleosol and fluvial incision 2 middle to late eocene relative baselevel rise and deposition of the cpf 3 late eocene relative baselevel fall weathering and erosion of the cpf to form the interior paleosol and fluvial incision and 4 late eocene to oligocene relative baselevel rise and deposition of the chadron formation the first event was probably eustatic the second was controlled primarily by local subsidence in a fault bounded basin the third records the tectonic uplift and unroofing of the black hills and the fourth event was probably primarily controlled by eustasy but other factors may have been important

tectonically controlled quaternary intracontinental fluvial sequence development in the nyirseg pannonian basin hungary abstract the quaternary fluvial succession of the nyirseg ne hungary a proximal sub basin of 4000 km2 in the intracontinental pannonian basin was studied based on log facies analysis regional mapping of sequences was established by analysis of fully cored boreholes and high scale local correlations in densely drilled areas the age of the sequences was determined by correlating the magnetic susceptibility ms record of the fully cored boreholes with that of the reference hungarian boreholes dated paleomagnetically devavanya 1 and veszt 1 in cooke et al 1979 to give the hungarian data global perspective they were correlated to the ms curve of the chinese loess ding et al 2005 that are in turn correlated with the marine isotope record lisiecki and raymo 2005 gibbard and cohen 2008 the ages of the mapped sequence boundaries are 2 62 2 26 2 12 1 22 1 04 0 58 and 0 34 ma respectively and can be related to the transitions from cool to warm conditions regional unconformities at 2 26 2 12 1 22 and 0 58 ma also coincide with activity maxima of the radiometrically dated quaternary volcanism this high frequency of climatically controlled erosive sequence boundaries in the structurally active periods indicates that the sedimentary record of climatic erosion is better expressed in times when structural changes generate instability in the drainage network the occurrence of packages of regional unconformities in relation to volcanic activity enables the geochronological dating of episodes in the quaternary compression of the carpathian pannonian region the role of tectonic control on the climatically induced changes in the drainage network has been explained by a structural development model based on seismic gravity and magnetic data the changes in the local paleohydrology were triggered by a compression related elevation of the basement and the associated occurrence of a local transtension related subsidence

mapping the mass distribution of earth s mantle using satellite derived gravity gradients the dynamics of earth s mantle are difficult to constrain analysis of goce satellite gravity data can be used to identify gravity anomalies to mid mantle depths and hence to identify regions of tectonic plate subduction and plume upwelling in the mantle

regional paleoprecipitation records from the late eocene and oligocene of north america abstract the marine 18o record indicates precipitous cooling or significant expansion of antarctic ice volume across the eocene oligocene epoch boundary at 33 7 ma this climatic step is also found in estimates of decreased paleoprecipitation from paleosols in oregon montana and nebraska but is only a part of a long term decline across the eocene oligocene transition rather than a sudden shift this suggests that climate was driven by a gradual process rather than a single perturbation paleoprecipitation levels stabilized during the oligocene coincident with a stabilization in 18o values possibly indicating a new climatic steady state

discontinuity bounded alluvial sequences of the southern gangetic plains india aggradation and degradation in response to monsoonal strength abstract discontinuity bounded late quaternary sequences in the southern gangetic plains himalayan foreland basin reflect floodplain aggradation and degradation in response to forcing by the powerful southwest indian monsoon the major himalayan and cratonic rivers in this area occupy narrow incised valleys and do not inundate the adjoining broad interfluves which display soil development small plains fed rivers lakes eolian deposits and badland ravines however these areas formerly experienced active alluviation because thick floodplain muds underlie the interfluve an age model suggests that interfluve areas near the major rivers aggraded periodically between about 27 ka and 90 ka marine oxygen isotope stages 3 5 they subsequently degraded or accumulated sediment only locally probably reflecting decreased monsoonal precipitation around the last glacial maximum marine isotope stage 2 when major river valleys moved to an underfit condition increased precipitation during the 15 to 5 ka period of monsoon recovery probably increased discharge and promoted incision and widespread badland formation discontinuities at deeper levels reflect earlier degradation phases and are marked by reworked gravel lenses thin channel bodies and carbonate cemented surfaces carbonate veins infilled joints that cut strata below but not above one discontinuity suggest some local tectonic influence there is no evidence that sea level fluctuations influenced stratal patterns in this elevated inland region discontinuity bounded sequences linked to climate change may characterize alluvial successions in many continental settings especially along the cratonic margins of foreland basins where subsidence rates are modest

intra arc crustal loading and its tectonic implications north cascades crystalline core washington and british columbia widespread high pressure cretaceous metamorphism in the coast plutonic complex of southeast alaska and british columbia and its southeast extension the cascades crystalline core is commonly attributed to thrust loading during superterrane collision however terrane boundaries within the cascades core are intruded by relatively shallow mid cretaceous plutons and crustal loading of 2 5 kbar postdates these plutons these observations are not consistent with proposed collisional models and we suggest that loading occurred by structural and or plutonic processes operating within a magmatic arc such loading may be an important process in arc tectonics although it has not been widely reported

late paleogene extensional collapse of the cordilleran foreland fold and thrust belt the cordilleran foreland fold and thrust belt collapsed and spread to the west during a middle eocene to early miocene ca 49 20 ma episode of crustal extension the sedimentary and structural record of this event is preserved in a network of half grabens that extends from southern canada to central utah extensional structures superposed on this allochthonous terrain are rooted to the physical stratigraphy structural relief and sole faults of preexisting thrust fold structures the sole faults dip 3 6 west above an undeformed precambrian crystalline basement and accommodated tectonic transport of a thick up to 20 km eastward tapering hanging wall during regimes of crustal shortening and extension the chronology of tectonism for the foreland fold and thrust belt is established here by dating latest thrusting and initial normal faulting and is best defined where thrusts and normal faults are linked by common detachment surfaces dated movement on two extensionally reactivated thrusts the lewis thrust of northwest montana and southeast british columbia and the medicine butte thrust of southwest wyoming and northeast utah suggests that the hiatus between the end of crustal shortening in the early or early middle eocene and the start of extension in the early middle eocene was brief lateral spreading and extensional basin formation in the cordilleran foreland fold and thrust belt were partly concurrent with formation of metamorphic core complexes and regional magmatism conceptually linking extensional processes that were simultaneously deforming both the hinterland and foreland of the late paleogene cordilleran orogenic wedge is accomplished by applying the extensional wedge coulomb critical taper model the rapid drop in north america pacific plate convergence rate and or steepening of the subducted oceanic slab at ca 50 ma resulted in a large reduction in east west horizontal compressive stress in the cordillera as a result the cordilleran orogenic wedge was left unsupported and it gravitationally collapsed and horizontally spread west until a new equilibrium was established at ca 20 ma subsequently crustal extension and magmatism during the basin and range event ca 17 0 ma overprinted much of this earlier phase of extension

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

structural geologic evolution of the butte district montana the butte district contains two porphyry cu mo deposits and the younger zoned main stage base metal lode deposits that formed in the period from 66 to 62 ma synchronous with laramide compressional thrust faulting and folding in southwest montana new geologic mapping of the butte district reveals three distinct episodes of deformation 1 gentle 20 10 ne tilting produced during laramide compressional deformation uplift and exhumation during and after ore formation in the late cretaceous to paleocene 66 53 ma 2 moderate 10 50 nw tilting of eocene age produced by ne striking normal faults that are limited to the northwest part of the district and synchronous with the eruption of the lowland creek volcanics and 3 miocene to present gentle 15 ese tilting in the hanging walls of the continental east ridge and rocker normal faults stratigraphic relationships isotopic ages hornblende barometry and fluid inclusion data indicate that exposures of the butte granite which hosts mineralization crystallized at 6 to 9 km depth and that early porphyry cu mo deposits formed at similar depths of 5 to 9 km a period of rapid uplift and erosion removed about 7 km of rock from above the ore deposit between 66 to 64 ma and 53 ma but was mostly completed by 59 ma estimated exhumation rates range from 0 5 to 2 mm yr and uplift was likely most rapid between 63 5 and 62 ma during main stage mineralization which occurred at depths of 2 to 6 km the butte granite and boulder batholith were emplaced at 79 to 76 ma into thrust fault ramps which later became inactive near butte as laramide crustal shortening moved eastward in the helena salient the accelerated period of uplift and unroofing is attributed to renewed deformation along the montana disturbed belt south of butte that uplifted the south end of the boulder batholith and produced 20 of gentle ne tilting episode i in the district the exhumation history of the deposit is therefore broadly contemporaneous with ore formation and is consistent with the general transition from lithostatic to hydrostatic conditions that is evident from the telescoping of early porphyry cu mo ores cut by the main stage lode veins within a 5 m y period the laramide compressional regime near butte evolved into an extensional environment characterized by normal faulting the normal faults were synchronous with eruption of the 53 to 48 ma lowland creek volcanics which directly overlie the main stage veins in the northwest part of the district structural reconstruction of the district at the time of mineralization produces orientations of quartz porphyry dikes porphyry cu mo veinlets main stage veins and alteration zonal patterns that are steeply dipping and symmetrical similar to observations from other upright or restored porphyry copper deposits early porphyry cu mo veins and dikes are oriented e w and likely originated as tensile hydrofractures above a ductile magma carapace during laramide shortening additionally during the laramide compressional phase two conjugate fault systems occupied by main stage veins are normal oblique slip faults that record minor e w and vertical shortening and n s extension these normal faults with minor offset likely resulted from brittle failure caused by doming above a volatile rich and buoyant granitic magma chamber and cupola at depth the structural evolution of the butte district therefore reflects the interaction of a far field compressive stress regime with local buoyant magmatic forces

basement and cover rock deformation during laramide contraction in the northern madison range montana and its influence on cenozoic basin formation two major laramide fault systems converge in the northwestern madison range the northwest striking southwest vergent spanish peaks reverse fault and the north striking east vergent hilgard thrust system analysis of foliation attitudes in basement gneiss north and south of the spanish peaks fault indicates that the basement in thrusted blocks of the hilgard thrust system has been rotated by an amount similar to that of the basement cover contact steeply dipping north striking breccia zones enclosing domains of relatively undeformed basement may have permitted domino style rotation of basement blocks during simple shear between pairs of thrusts in most places along the hilgard thrust system a large basement overhang produced by thrusting of archean blocks above rocks as young as late cretaceous overlies a tight footwall syncline this tight folding is largely concentric and was accommodated by flexural slip resulting in severe crowding in synclinal hinges that resulted in observed or inferred features such as bedding plane slip imbricate and out of syncline thrusting and hinge collapse the north striking madison normal fault system a zone of tertiary and quaternary valley forming normal faults is approximately parallel to the hilgard thrust system in some places normal faults are reactivated thrusts on which large basement overhangs of the hilgard thrust system were dropped back into the madison valley and covered by tertiary basin fill deposits leaving only the rocks of the footwall synclines exposed in other places both the thrusted archean blocks and the near isoclinal footwall synclines are well preserved this paired fault system the madison normal fault system and the hilgard thrust system of the northern madison range is strikingly similar to other paired systems in southwestern montana along and adjacent to the western margins of the ruby range snowcrest range greenhorn range tobacco root mountains and bridger range such systems may be the result of collapse of the crestal zones of large laramide basement uplifts arches during tertiary extension no hydrocarbon discoveries have been made in this unique structural province however petroleum exploration here has focused on basement cored anticlines both surface and subthrust related to the two major laramide fault systems and on the fault bounded blocks of tertiary rocks within the post laramide extensional basins the interplay of the two laramide fault systems during both laramide shortening and tertiary extension has produced a variety of possible structural traps in the madison range that have not yet been thoroughly investigated