erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

geochemical investigations of selected eastern united states watersheds affected by acid deposition the effects of acid deposition on surface waters in eastern united states watersheds having similar size physiography climate and land use are related to the composition of the underlying bedrock watersheds developed on greenstone calcareous shale sandstone granite and schist differ in their ability to neutralize acid deposition surface waters in watersheds developed on greenstone and calcareous shale are not discernably affected by acidification wastersheds developed on sand stone have little capacity to neutralize acid rain consequently stream acidity is similar to that of precipitation watersheds developed on granite and schist are intermediate in their capacity to neutralize acid deposition bedrock composition appears to be the major property controlling surface water chemistry in these systems hydrologic flow paths and the nature of surficial materials and vegetation also influence chemical responses to acid deposition in watersheds

reply to comment by hillis et al 2013 we agree that there is now convincing evidence which favours the idea that a region encompassing the british isles is dynamically supported by convective circulation beneath the lithospheric plate for example the coincidence of a long wavelength 800 km free air gravity anomaly with anomalously slow velocities beneath the lithospheric plate suggests that regional elevation of northern britain is maintained by a tongue of hot asthenosphere protruding away from iceland jones et al 2002a arrowsmith et al 2005 these observations are corroborated by the crustal thickness measurements of davis et al 2012 the icelandic plume initiated 62 ma and there is excellent evidence in the irminger and icelandic basins that this plume has waxed and waned with different periodicities jones et al 2002b poore et al 2009 this transient activity has manifest itself in geochemical and earthquake records along the reykjanes ridge poore et al 2011 parnell turner et al 2013 in the neogene record of deep water overflow across the greenland scotland ridge poore et al 2006 and along the fringing continental margins where spectacular buried ephemeral landscapes have been encountered shaw champion et al 2008 rudge et al 2008 hartley et al 2011 around the british isles there is considerable onshore and offshore evidence favouring a history of transient and or permanent vertical motions which may reflect palaeogene and neogene plume activity white lovell 1997 jones et al 2001 jones et al 2002a al kindi et al 2003 jones white 2003 mackay et al 2005 this regional pattern of epeirogeny is locally complicated by faulting and folding which is often difficult to date with precision

geophysical evidence concerning the southern boundary of the london platform beneath the hog s back surrey the results of a gravity survey have been interpreted with seismic reflection and borehole data to show that a major change in the structure of the upper crust underlies the hog s back w of guildford surrey the pre mesozoic basement beneath the thin mesozoic succession n of the hog s back is of a lower density than that underlying the thick mesozoic succession to the s this lower density basement was probably the principal cause of the relative stability of the london platform during the mesozoic era the sourthern boundary of the london platform may have been initiated by variscan thrusting with subsequent reversal of displacement or may be inherited from an older crustal lineament

appalachian piedmont landscapes from the permian to the holocene abstract between the potomac and susquehanna rivers and from the blue ridge to the fall zone landscapes of the piedmont are illustrated for times in the holocene late wisconsin early miocene early cretaceous late triassic and permian landscape evolution took place in tectonic settings marked by major plate collisions permian arching and rifting late triassic and development of the atlantic passive margin by sea floor spreading early cretaceous erosion proceeded concurrently with tectonic uplift and continued after cessation of major tectonic activity atlantic outer continental shelf sediments record three major erosional periods 1 late triassic early jurassic 2 late jurassic early cretaceous and 3 middle miocene holocene the middle miocene holocene pulse is related to neotectonic activity and major climatic fluctuations in the piedmont upland the holocene landscape is interpreted as an upland surface of low relief undergoing dissection major rivers and streams are incised into a landscape on which the landforms show a delicate adjustment to rock lithologies the fall zone has apparently evolved from a combination of warping faulting and differential erosion since late miocene the periglacial environment of the late wisconsin and earlier glacial epochs resulted in increased physical erosion and reduced chemical weathering even with lowered saprolitization rates geochemical modeling suggests that 80 m or more of saprolite may have formed since late miocene this volume of saprolite suggests major erosion of upland surfaces and seemingly contradicts available field evidence greatly subdued relief characterized the early miocene time near the end of a prolonged interval of tropical morphogenesis the ancestral susquehanna and potomac rivers occupied approximately their present locations in early cretaceous time local relief may have been as much as 900 m and a major axial river draining both the piedmont and appalachians flowed southeast past baltimore the late triassic landscape was influenced by rift basin development streams drained into a hydrologically closed basin no through flowing rivers seem to have been present a limestone escarpment along the blue ridge may have existed as a consequence of a semi arid climate the permian may have been a time of himalayan like mountains and mountain glaciers streams and glaciers generally flowed southwest and west

aspects of basin inversion in southern britain the wessex basin of southern england a permian to cretaceous extensional basin can be structurally divided into a set of constituent asymmetrical graben bounded by major e w trending zones of en echelon syn depositional normal faults the graben were inverted in late cretaceous and tertiary times by compressive stresses oriented roughly north south inversion structures fall into two related categories regional upwarps overlie earlier graben depocentres and were formed by bulk shortening of the graben fill superimposed upon and geographically delimiting the regional upwarps are roughly east west trending linear zones of en echelon inversion structures these coincide with the earlier graben bounding faults and typically have the form of monoclinal or periclinal flexures each underlain by a partially reversed normal fault the linear reverse fault monocline inversion structures were a relatively inefficient method of basin shortening because upper crustal faults in the region steepen upward markedly reversal of these faults under compression resulted in a shortening discrepancy at shallow depths locally particularly in south dorset this was overcome by bucklefolding and low angle reverse faulting which increased the amount of shortening attainable across the linear inversion structures elsewhere however the shortening discrepancy was accommodated by bulk shortening and regional upwarp of the graben sedimentary fill this occurred preferentially in those graben containing young poorly lithified and therefore weak sediments thus the early cretaceous depocentres of the weald and channel basins were strongly upwarped with axial uplifts of over 1000 m conversely graben having older more lithified sequences suffered little regional upwarp shortening primarily by fault reversal along the linear inversion structures the amount of crustal shortening which accompanied inversion was considerably less than the earlier crustal extension

origin of late cements in oolitic reservoir facies a fluid inclusion and isotopic study mid jurassic southern england abstract during bathonian times a carbonate ramp was constructed over southern england by the progradation of oolitic skeletal and oncoidal grainstones and packstones the grainstones provide a significant hydrocarbon reservoir facies although these carbonates suffered early diagenesis under marine and more significantly meteoric conditions later diagenetic cements such as saddle dolomite and more particularly mildly ferroan calcite are volumetrically more important in causing the occlusion of porosity on a regional scale we have analysed systematically these late cements employing a number of techniques standard petrography including cl and uvl c and o isotopes sr isotopes and fluid inclusion studies integration of the results of these approaches constrains both the pore fluid composition and the temperature regime at the time of cement precipitation saddle dolomite was emplaced before the mildly ferroan calcite at temperatures between 75 and 85 c and from highly saline brines 18 19 5 wt nacl equivalents mildly ferroan calcite precipitated over a generally lower temperature range and from less saline brines 6 5 15 wt nacl equivalents five types of fluid inclusion have been recognised 1 monophase aqueous liquid 2 monophase oil liquid 3 two phase aqueous liquid vapour 4 two phase oil liquid hydrocarbon vapour 5 three phase aqueous oil liquid hydrocarbon aqueous liquid vapour during burial warm 75 c brines passed through the limestones and precipitated saddle dolomite later slightly cooler oil rich brines precipitated mildly ferroan calcite wherever hydrocarbon accumulation had not already occurred our sr isotopic studies suggest that both these brines were derived from underlying and more deeply buried lias shales and that these brines were generated from late jurassic times onwards brine movements are likely to have been largely complete by the late cretaceous

heat flow and thermal conductivity measurements in the northeastern pennsylvania appalachian basin depocenter the northern appalachian basin depocenter of pennsylvania represents one of the most economically important hydrocarbon producing areas in the united states yet the thermal conditions that promoted hydrocarbon formation within the basin are only marginally constrained the prolific coal oil and natural gas fields of pennsylvania are the direct result of thermal maturation of once deeply buried organic rich sediment understanding how why and where thermal maturation occurred in the appalachian basin requires high quality heat flow and thermal conductivity measurements as well as paleotemperature estimates and basin modeling to improve the understanding of heat flow we present to our knowledge the first direct measurements of 1 thermal conductivity on devonian core samples and 2 equilibrium temperature versus depth logs for the northern appalachian basin depocenter results from three well sites demonstrate that heat flow is conductive and nearly uniform averaging 34 2 5 mw m2 with an average thermal gradient of 29 4 c km the new heat flow measurements are significantly lower 30 50 less than previously published estimates that used nonequilibrium bottomhole temperature values and empirically derived thermal conductivity estimates our analysis indicates that previous studies correctly estimated the regional thermal gradient using bottomhole temperatures but overestimated heat flow in this region by as much as 50 because of inaccurate extrapolation of thermal conductivity the results highlight the importance of directly measuring thermal conductivity to accurately quantify heat flow in deep sedimentary basins ultimately additional paleotemperature data are necessary to improve our understanding of appalachian basin thermal evolution

detailed 3 d depositional architecture of late jurassic carbonate anhydrite cycles brightling mine weald basin uk abstract quantifying the geometries of evaporite deposits at a 13 c and 18 o isotope analysis the stratigraphic interval contains five facies in stratigraphic order these include supratidal porphyritic nodular evaporite shallow subtidal peloidal packstone with evaporite and two overlying rhythmic sequences of intertidal microbial laminite subtidal shale and subtidal laminar marl capped by nodular anhydrite the interpreted environment of deposition is a supratidal sabkha subject to periodic flooding in which intertidal tidal flat facies and subtidal shallow marine facies laterally passed into the evaporative sabkha the cycles are interpreted as meter scale shoaling upward sequences likely controlled by localized high frequency changes in relative sea level and or sabkha hydrology spatial patterns in the geometries of key stratigraphic surfaces reveal a subtle depression towards the central western region of the mine seam the variation in stratal geometries is interpreted as paleotopography and is a function of individual or composite processes related to dissolution eolian processes and coastal erosion these observations indicate a similar mode of deposition to the modern day sabkha of the persian gulf we conclude that the dynamic process of evaporite deposition led to subtle stratigraphic heterogeneities and changes in bed thicknesses but largely continuous lateral bedding at an interwell scale

migration of orogenic fluids through the siluro devonian helderberg group during late paleozoic deformation constraints on fluid sources and implications for thermal histories of sedimentary basins abstract fluid inclusion data and fracture filling cement fabrics in deformed but non overthrusted carbonate and siliciclastic rocks of the siluro devonian helderberg group central appalachians indicate post cementation late paleozoic migration of high pressure high temperature fluids void filling quartz and calcite cements contain secondary two phase fluid inclusions liquid vapor which occur in annealed microfractures most melting temperatures last occurrence of ice are 20 to 25 c which correspond to salinities of greater than 22 equivalent wt nacl pressure corrected liquid vapor homogenization temperatures are 200 to 300 c and greatly exceed maximum paleotemperatures 150 c given by conodont cai values vitrinite reflectance illite crystallinity or temperatures calculated from known sedimentary overburden completely cemented sandstone and limestone also have multiple crosscutting trains of secondary hydrocarbon inclusions hydrocarbon inclusions occur along deformation microstructures in cements some hydrocarbon inclusion trains crosscut cement filled fractures the nature of occurrence of the secondary inclusions suggests that fluids moved along intracrystalline deformation microstructures either during or after late paleozoic deformation rare fractures contain transported skeletal grains exotic clasts lithologies different from wall rock recemented clasts of fracture filling cement and mud cement clasts contain solid inclusions of mud and skeletal fragments and indicate several episodes of particle transport cementation and refracturing prior to final fracture filling and cementation these fracture fills locally crosscut stylolites coarse grained poorly sorted clastic fracture fills suggest migration of rapidly moving fluids which were capable of transporting clasts through fracture conduits under deep burial conditions conduction calculations place upper limits on size and duration of thermal anomalies which were caused by extrabasinal fluids these calculations indicate that hot fluid migration events most likely were short lived heat transfer by extraformational fluids moving along faults and fractures may have been the mechanism by which thermal anomalies developed in the helderberg group stratigraphic constraints suggest that likely sources for the hot brines are overthrusted terranes to the east of the study area possible stratigraphic horizons which were sources for the overpressured hot fluids may have been thick cambrian shales which are important detachment horizons for major late paleozoic thrust sheets in the eastern valley and ridge province east of the study area fluids may have migrated during thrusting along thrust faults which ramp upwards from east to west into stratigraphically higher units thrust faults ultimately die out in devonian units some of the dissolved ions in the secondary two phase inclusions may have been incorporated when shale derived fluids moved through silurian evaporites or cambro ordovician carbonates which contain evidence of cryptic evaporites potential source rocks for secondary hydrocarbon inclusions may have been lower silurian through lower devonian strata based on lopatin modeling and assuming that migration occurred during late paleozoic deformation this study may help to explain many apparently anomalous geologic phenomena in deformed foreland basin sediments it also has implications for tracking migration pathways for fluids which facilitate regional scale deformation in fold and thrust belts and how tectonic fluids may affect the rocks through which they move

brittle tectonic structures and palaeostress analysis in the isle of wight wessex basin southern u k abstract brittle tectonic analysis of cretaceous paleogene sediments at a total of 17 sites located in the isle of wight u k enables four main tectonic events that occurred prior to and after the folding to be identified and successive palaeostress tensors to be determined using the inversion method three of the events can be shown to have occurred prior to the folding 1 a syn sedimentary extension of upper cretaceous age 2 a strike slip faulting regime with an ese wnw direction of compression 3 a compressional regime marked by strike slip faulting with an nne ssw to n s direction of compression the fourth and last compressional event took place after the folding and is characterised both by reverse and strike slip faulting with a dominant n s direction of compression syn folding faults also developed between the third and fourth events all four events can be connected to the extensional tectonics and different steps of structural inversion both of which were integral to the development and evolution of the wessex basin

carbonate versus silicate weathering in the raikhot watershed within the high himalayan crystalline series the major element and sr isotope geochemistry of surface waters bedrock and river sands was investigated in the raikhot watershed within the high himalayan crystalline series hhcs in northern pakistan mass balance calculations of mineral weathering contributions to the dissolved flux of ions from the watershed indicate that 82 of the hco 3 flux is derived from the weathering of carbonate minerals and only 18 is derived from silicate weathering even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only 1 carbonate in the watershed this study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds we suggest that the flux of sr with a high 87 sr 86 sr ratio in the major himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate hhcs models that use the flux of radiogenic sr from the himalayas as a proxy for silicate weathering rates may therefore overestimate the amount of co 2 consumption due to silicate weathering in the himalaya

organic matter hosted pore system marcellus formation devonian pennsylvania the marcellus formation of pennsylvania represents an outstanding example of an organic matter om hosted pore system most pores detectable by field emission scanning electron microscopy fe sem are associated with om instead of mineral matrix in the two wells studied here total organic carbon toc content is a stronger control on om hosted porosity than is thermal maturity the two study wells span a maturity from late wet gas vitrinite reflectance ro 1 0 to dry gas ro 2 1 samples with a toc less than 5 5 wt display a positive correlation between toc and porosity but samples with a toc greater than 5 5 wt display little or no increase in porosity with a further increasing toc in a subset of samples 14 across a range of toc 2 3 13 6 wt the pore volume detectable by fe sem is a small fraction of total porosity ranging from 2 to 32 of the helium porosity importantly the fe sem visible porosity in om decreases significantly with increasing toc diminishing from 30 of om volume to less than 1 of om volume across the range of toc the morphology and size of om hosted pores also vary systematically with toc the interpretation of this anticorrelation between om content and sem visible pores remains uncertain samples with the lowest om porosity higher toc may represent gas expulsion pore collapse that was more complete as a consequence of greater om connectivity and framework compaction whereas samples with higher om porosity lower toc correspond to rigid mineral frameworks that inhibited compactional expulsion of methane filled bubbles alternatively higher toc samples may contain om low initial hydrogen index relatively unreactive that is less prone to development of fe sem detectable pores in this interpretation om type controlled by sequence stratigraphic position is a factor in determining pore size distribution

cement distribution in a carbonate reservoir recognition of a palaeo oil water contact and its relationship to reservoir quality in the humbly grove field onshore uk abstract the distribution of mineral cements total porosity microporosity and permeability have been determined for the humbly grove oolitic carbonate reservoir middle jurassic great oolite formation weald basin onshore uk using a combination of optical petrography electron microscopy fluid inclusion analysis quantitative xrd wireline data analysis and core analysis data grainstone reservoir facies have porosities ranging between 5 and 24 but are mostly between 11 and 24 permeabilities vary from

crustal structure beneath southern england from deep seismic reflection profiles seismic reflection events from recently acquired profiles in southern england are interpreted in terms of stratigraphic and structural interfaces between rock units in particular evidence is brought forward that a series of reflection events dipping between 22 and 27 with azimuth averaging 160 represents 2 major thrust zones occurring in the variscan floor beneath mesozoic cover a geological model based upon borehole information and regional geological considerations is presented the tentative recognition of crystalline basement overlain and overstepped by late proterozoic rocks of variable thickness suggests that basement in this area was unstable from late precambrian times the mesozoic structural evolution can be related to tectonic re activation of major concealed thrust zones in the palaeozoic 9basement9

chemical weathering in two adirondack watersheds past and present day rates rates of chemical weathering in two forested adirondack watersheds were determined from mineral and elemental depletion trends in soil profiles and from input output budgets based on precipitation and surface water chemistry long term rates of weathering have averaged about 500 to 600 eq ha yr for both watersheds since the glaciers retreated from the region about 14 000 yr ago present day denudation rates average 1679 eq ha yr in the panther lake watershed and only 198 eq ha yr in the woods lake watershed mineral weathering reactions in both watersheds involve primarily the dissolution of plagioclase potassium feldspar and hornblende mass balance calculations however indicate that hornblende weathers in disproportionately large amounts in the panther lake watershed relative to its abundance in soils and till cation exchange in the glacial till mantling the panther lake watershed may also play an important role in controlling surface water chemistry in the basin in the panther lake watershed the current rate of weathering which is about a factor of 3 greater than the long term average may reflect a recent adjustment for higher hydrogen ion fluxes brought about by acid deposition the capacity of the thick till deposits in the panther lake watershed to neutralize acidity is ultimately reflected by the circum neutrality of panther lake in the woods lake watershed the soils and thin till deposits cannot effectively neutralize current acid loadings and therefore woods lake is acidic with a ph below 5

sharp decrease in long term chemical weathering rates along an altitudinal transect we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and physical erosion across a steep climatic gradient in the santa rosa mountains nevada our study sites are distributed along a 2 km ridgeline transect that spans 2090 to 2750 m in altitude and encompasses marked contrasts in both vegetative cover and snow depth but is underlain by a single roughly uniform granodiorite bedrock cosmogenic nuclides in colluvial soils reveal that denudation rates vary by less than a factor of 1 4 104 144 t km2 yr along this transect bulk elemental analyses indicate that relative to the parent rock soils are less intensively weathered with increasing altitude and show little evidence of weathering related mass losses near the top of the ridge chemical weathering rates decrease rapidly with increasing altitude both in absolute terms from 24 to 0 t km2 yr and as a fraction of total denudation rates from 20 to 0 thus these results indicate an increasing dominance of physical erosion with altitude the observed decrease in chemical weathering rates is greater than one would predict from the decrease in mean annual temperature using simple weathering kinetics suggesting that weathering rates along our transect may also be affected by the progressive decline in vegetative cover and increase in snow depth with increasing altitude these results considered together with weathering rate measurements for a wide range of climates in the sierra nevada usa suggest that chemical weathering rates may be particularly sensitive to differences in climate at higher altitude sites consistent with this hypothesis chemical weathering rates fall virtually to zero at the highest sites on our transect suggesting that sparsely vegetated high altitude crystalline terrain may often be characterized by extremely slow silicate weathering rates

comment on crustal structure of the british isles and its epeirogenic consequences by m w davis n j white k f priestley b j baptie and f j tilmann while davis et al provide convincing evidence for dynamic support of modern topography in nw scotland we take issue with their claims that the spatial distribution of cenozoic denudation correlates poorly with the pattern of upper crustal shortening and that the magnitude of shortening is insufficient to cause the observed denudation we disagree with davis et al s map of denudation which forms the basis of their claims and believe that their conclusions seriously downplay the widely documented contribution of crustal shortening to cenozoic denudation of many areas of the british isles

chemical weathering in granitic environments abstract factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature based on a transition state theory model we evaluated the effects on chemical weathering of runoff temperature and ph the dependence between temperature and runoff and chemical weathering is complicated by other factors such as the presence depth of soil cover soil cover favors chemical weathering when it is thin and rich in weatherable minerals in contrast it reduces chemical weathering when is thick and poor in primary minerals processes that increase the contact time and the surface of the water rock interactions such as physical denudation increase chemical weathering rates in granitic environments the effect of temperature can be quantified assuming an apparent activation energy value of 48 7 kj mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions

mineralogic controls on the composition of natural waters dominated by silicate hydrolysis a detailed mineral solute mass balance spreadsheet model has been developed to improve understanding of mineralogic controls on water composition in surface waters and groundwater systems dominated by silicate lithologies the spreadsheet based approach is used to investigate mass balance solutions over a range of mineral compositions for predominant multi element phases such as plagioclase biotite chlorite amphibole and dioctahedral smectite the mass balance technique has been applied to a variety of hydrogeologic environments including calibrated watersheds springs and groundwater systems lithologic settings include plutonic metamorphic minor volcanic and sedimentary alluvial and glacial deposits materials sites investigated most of which allowed comparison with earlier work include ephemeral and perennial springs of the central sierra nevada mountains california the loch vale colorado high altitude watershed four catchments in the inyo mountains california and nevada watersheds in the catoctin mountain maryland area and ground water flow systems in vekol valley arizona and in the trout lake area wisconsin analytical mass balances were derived with a novel approach that permits graphic analysis of the functional dependency of mineral mass transfer coefficients on variations in major silicate composition a 10 x 10 matrix of mineral solute reaction equations was used to solve for the best mass balances alternative methods were developed to investigate cases where the number of mineral phases exceeds the number of solute constraints 10 that are commonly found in clastic silicate dominated systems with diverse sources and or phase mixtures of variable chemistry such as an assortment of plagioclase compositions techniques were also developed to allow for important structurally controlled compositional variation in clay minerals final mass balance choices were tempered by thermodynamic stability calculations for various minerals under near surface weathering conditions mineral mass transfer ratios were also found to be useful in restricting mass balances additional constraints were provided by establishing consistent sets of similar mineral assemblages and mineral compositions for a series of wells along a ground water flow path or through comparison of multiple nearby watersheds subject to similar climatic and vegetative conditions whereas unique analytical solutions from spreadsheet mass balances were not always possible a surprisingly limited range was obtained for mineral assemblages and compositions satisfying observed mineral occurrences and thermodynamic stability conditions our results demonstrate the importance of having well characterized mineral compositions for both reactant and product phases the mass balance results are particularly sensitive to the compositions of plagioclase dioctahedral smectite and a few primary mafic mineral groups trioctahedral mica amphibole and pyroxene in addition to mineral controls the specific examples studied demonstrate effects of dolomite and calcite overprints on silicate weathering biomass fluctuations road salt contamination and on buried evaporite salts a comparison of the mass balance results from surface and groundwater systems indicates strong similarities suggesting that similar processes dominate the mineral controls in both settings and that under soil weathering conditions ion exchange might have been overemphasized except under conditions where pre existing waters are displaced by solutions of significantly different composition

determining rates of chemical weathering in soils solute transport versus profile evolution abstract sio 2 fluxes associated with contemporary solute transport in three deeply weathered granitoid profiles are compared to bulk sio 2 losses that have occurred during regolith development climates at the three profiles range from mediterranean to humid to tropical due to shallow impeding alluvial layers at two of the profiles and seasonally uniform rainfall at the third temporal variations in hydraulic and chemical state variables are largely attenuated below depths of 1 2 m this allows current sio 2 fluxes below the zone of seasonal variations to be estimated from pore water concentrations and average hydraulic flux densities mean annual sio 2 concentrations were 0 1 1 5 mm hydraulic conductivities for the investigated range of soil moisture saturations ranged from 9 to 10 6 m s 1 estimated hydraulic flux densities for quasi steady portions of the profiles varied from 6 10 9 to 14 10 9 m s 1 based on darcy s law and field measurements of moisture saturations and pressure heads corresponding fluid residence times in the profiles ranged from 10 to 44 years total sio 2 losses based on chemical and volumetric changes in the respective profiles ranged from 19 to 110 kmoles sio 2 m 2 of land surface as a result of 0 2 0 4 ma of chemical weathering extrapolation of contemporary solute fluxes to comparable time periods reproduced these sio 2 losses to about an order of magnitude despite the large range and non linearity of measured hydraulic conductivities solute transport rates in weathering regoliths can be estimated from characterization of hydrologic conditions at sufficiently large depths the agreement suggests that current weathering rates are representative of long term average weathering rates in the regoliths

distribution of maximum burial temperatures across northern appalachian basin and implications for carboniferous sedimentation patterns clay mineral diagenesis and apatite fission track age data indicate that the maximum burial temperatures to which the middle devonian tioga metabentonite was exposed rise abruptly from low values in western new york state to higher values in the east the highest temperatures which approach 175 sup 0 c were reached just west of syracuse neither the pattern nor the magnitude of burial temperatures can be explained solely by burial of the metabentonite beneath upper devonian sediments although spatial variations in the geothermal gradient could have produced the observed pattern of burial temperatures it is more likely that carboniferous sediments no longer preserved in the area were responsible for the indicated burial the inferred presence of thick carboniferous sequences in western new york state suggests that the allegheny orogeny had a stronger influence on sedimentation in the northern appalachian basin than has been previously recognized 25 references 2 figures 2 tables

geochemical mass balances and weathering rates in forested watersheds of the southern blue ridge ii effects of botanical uptake terms abstract geochemical mass balance methods are commonly used in small watershed studies to estimate rates of primary mineral weathering and soil formation and the contribution of these processes to cation budgets nutrient cycling and landscape susceptibility to acid deposition many researchers employ the balance sheet approach a system of simultaneous linear equations with constant coefficients which represent the steady state behavior of the modelled system most workers also assume that the steady state assumption for the entire system means that botanical factors can be ignored in other words that there is no net elemental transfer between biomass and inorganic compartments of the system however the widely invoked assumption that biomass is at steady state is mathematically a second explicit assumption not a built in mathematical consequence of the assumption of overall steady state the common assumption that the biomass is necessarily at steady state in a steady state system ignores the possibility of uptake of elements into the forest biomass to quantify the implications of the separate mathematical assumptions weathering rates for seven forested watersheds in the southern blue ridge mountains are calculated twice once allowing for net element exchange with biomass and once assuming no net exchange with biomass our calculations show that misunderstanding the mathematical constraints which are built into the most widely used geochemical mass balance equations commonly causes errors underestimates of up to a factor of 4 in the calculated rates of mineral weathering and soil formation this problem is most pronounced for minerals which contain major nutrient elements and for rates calculated from mass balances of those nutrient elements

early diagenetic formation of carbonates in a clastic dominated ramp environment impacted by synsedimentary faulting induced fluid seepage evidence from the late jurassic boulonnais basin n france the late jurassic deposits of the boulonnais area n france represents the proximal lateral equivalent of the kimmeridge clay formation they accumulated on a clastic dominated ramp subject to synsedimentary faulting in relation with the northward propagation of the atlantic rifting within the terrigenous accumulations some carbonate objects are visible at various conspicuous levels oyster patch reefs and fine grained carbonate beds either continuous or more or less nodular preliminary studies demonstrated that the carbonate beds of the bancs jumeaux formation as well as the carbonate matrix of the oyster patch reefs are of diagenetic origin in this paper we extend the study to many other limestone beds of the boulonnais with mud or wackestone texture examining facies and microfacies through various techniques as well as geochemical data o c and s stable isotopes major and trace elements we conclude that all examined carbonate bodies are of early diagenetic origin and that they precipitated at or close to the sea bed from seawater mixing with ascending fluids containing isotopically light carbon of organic origin fluid circulation was probably induced by the extensional block faulting segmentation of the northern margin of the boulonnais basin in late jurassic times fluid seepages were either channelized along fault planes or more diffuse as illustrated by the model we propose

lithologic and climatologic controls of river chemistry abstract the chemistries of rivers draining a variety of lithologic and climatic regions have been surveyed for the purpose of quantifying the fluxes of bicarbonate and silica from rivers with respect to bedrock lithology and runoff in all 101 different rivers each draining a primary lithology were examined across the united states puerto rico and iceland to minimize seasonal effects only rivers with at least two years of data were used basaltic catchments were examined in the greatest detail in a survey of hawaiian island watersheds the average river chemistries could be related to the distribution of soil associations within each catchment an analysis of cation activity relationships among rivers draining basaltic catchments shows that the river compositions define slopes which are consistent with an equilibrium ion exchange control on cation ratios among different lithologies unique weathering rate relationships were developed with yields at typical present day runoff rates 1 100 cm y increasing in the order sandstones granites basalts shales and carbonates the bicarbonate and silica fluxes for each of these lithologies have been quantified for use in global studies of chemical denudation our study confirms that the dissolved yield of a given drainage basin is determined by a balance between physical and chemical weathering thus a warm wet climate or the presence of abundant vegetation cannot guarantee high rates of chemical denudation unless accompanied by high rates of physical removal

mass balance modeling of mineral weathering rates and co2 consumption in the forested metabasaltic hauver branch watershed catoctin mountain maryland usa mineral weathering rates and a forest macronutrient uptake stoichiometry were determined for the forested metabasaltic hauver branch watershed in north central maryland usa previous studies of hauver branch have had an insufficient number of analytes to permit determination of rates of all the minerals involved in chemical weathering including biomass more equations in the mass balance matrix were added using existing mineralogic information the stoichiometry of a deciduous biomass term was determined using multi year weekly to biweekly stream water chemistry for a nearby watershed which drains relatively unreactive quartzite bedrock at hauver branch calcite hosts 38 mol of the calcium ion ca2 contained in weathering minerals but its weathering provides 90 of the stream water ca2 this occurs in a landscape with a regolith residence time of more than several ka kiloannum previous studies indicate that such old regolith does not typically contain dissolving calcite that affects stream ca2 na ratios the relatively high calcite dissolution rate likely reflects dissolution of calcite in fractures of the deep critical zone of the carbon dioxide co2 consumed by mineral weathering calcite is responsible for approximately 27 with the silicate weathering consumption rate far exceeding that of the global average the chemical weathering of mafic terrains in decaying orogens thus may be capable of influencing global geochemical cycles and therefore climate on geological timescales based on carbon balance calculations atmospheric derived sulfuric acid is responsible for approximately 22 of the mineral weathering occurring in the watershed our results suggest that rising air temperatures driven by global warming and resulting in higher precipitation will cause the rate of chemical weathering in the hauver branch watershed to increase until a threshold temperature is reached beyond the threshold temperature increased recharge would produce a shallower groundwater table and reduced chemical weathering rates copyright 2013 john wiley sons ltd

mapping hydrocarbon charge points in the wessex basin using seismic geochemistry and mineral magnetics abstract this study reports a multidisciplinary approach to determining hydrocarbon charge points and migration in the wessex basin southern england geochemical analysis of reservoir core material bridport sandstone and inferior oolite using gas chromatography mass spectrometry gc ms suggests that the oil in the wessex basin is from a single source and that small variations in environmentally sensitive biomarkers are likely due to small differences in maturity or depositional conditions during the formation of the oil over millions of years using seismic data basin modelling revealed two potential hydrocarbon migration pathways from the hanging wall of the purbeck fault into the sherwood sandstone reservoir at wytch farm one of these potential pathways is represented by cores termed creech and the other bushey farm to try to distinguish between the two potential pathways cores were studied using mineral magnetic techniques the magnetic signature was characterised using low temperature

the effect of land plants on weathering rates of silicate minerals abstract land plants and their associated microbiota directly affect silicate mineral weathering in several ways by generation of chelating ligands by modifying ph through production of co2 or organic acids and by altering the physical properties of a soil particularly the exposed surface areas of minerals and the residence time of water in laboratory experiments far from equilibrium 1 mm oxalate a strong chelator of al has a negligible effect on the dissolution rate of alkali feldspars but some effect on calcic feldspars and olivine by analogy to oxalate the overall effect of organic ligands on the weathering rate of silicate minerals in nature is likely to be small except perhaps in microenvironments adjacent to roots and fungal hyphae the effect of ph on silicate mineral dissolution rate depends on ph below ph 4 5 the rate increases with decreasing ph in the circumneutral region the rate is ph independent and at ph values above around 8 the rate increases with increasing ph vegetation should thus cause an increase in weathering rate through the ph effect only where the ph is below 4 5 as an overall generalization the effect of plants on weathering rate through changes in soil solution chemistry is probably small for granitic rocks it may be greater for more mafic rocks it is the release of ca and mg from mafic rocks that has the greatest influence on the global co2 budget the effect of changes in soil physical properties on weathering rate can be major by binding fine particles plants can greatly increase weathering rates in areas of high physical erosion where erosion rates are lower the effect of plants is less clear on long timescales plants may decrease chemical weathering by binding secondary products and isolating unweathered minerals from meteoric water a major unknown in estimating the effect of the advent of land plants on weathering rates is the nature thickness particle size distribution permeability of the regolith on the pre silurian continents the indirect effect of vegetation through changing the regional distribution of precipitation may be as important as the direct effects

rates and time scales of clay mineral formation by weathering in saprolitic regoliths of the southern appalachians from geochemical mass balance rates of clay formation in three watersheds located at the coweeta hydrologic laboratory western north carolina have been determined from solute flux based mass balance methods a system of mass balance equations with enough equations and unknowns to allow calculation of secondary mineral formation rates as well as the more commonly determined primary mineral dissolution rates was achieved by including rare earth elements ree in the mass balance rates of clay mineral formation determined by mass balance methods have been used to calculate the time needed for a 5 50 g kg 1 change in relative clay abundance in the saprolite at coweeta this corresponds to the response time of the clay mineral to for example a change in climate the 5 change in relative clay abundance is the smallest change that can generally be detected using x ray diffraction xrd response times range from tens of thousands to hundreds of thousands of years extrapolating the coweeta clay formation rates to other southern appalachian regoliths the time required to form measured clay abundances production times in eastern blue ridge and inner piedmont regolith have been calculated the production times of clay mineral assemblages range from 2 k y to 2 m y with mean values ranging from 50 k y to 1 m y the results of this study are consistent with the arguments of thiry 2000 1 that the best resolution of the paleoclimatic record in marine clay rich sediments and mudrocks is 1 or 2 m y 1 ref 107

long term average mineral weathering rates from watershed geochemical mass balance methods using mineral modal abundances to solve more equations in more unknowns abstract the number of phases for which weathering rates can be determined by watershed geochemical mass balance is limited by the number of equations that can be constructed from elemental flux losses from the watershed and mineral stoichiometries mass balance studies of watershed weathering rates routinely use the flux losses of the six major cations sio 2 al na k mg and ca analyses of these species in water are common but following matrix algebraic methods limits the number of weathering rates that can be calculated to six for the brubaker run watershed located in the northern piedmont physiographic province of pennsylvania usa long term 10 3 10 6 year watershed chemical flux losses have been determined using 10 be derived total denudation rates and zirconium normalized total chemical concentrations from bedrock and soils chemical flux losses calculated from solid phase data have three advantages they 1 permit generation of a relatively large number of equations because both major and trace analyses are included 2 eliminate the need for many years of regular e g weekly sampling and chemical analyses of stream water and atmospheric precipitation and measurement of hydrologic parameters i e precipitation stream discharge etc and 3 long term weathering rate calculations need not address biomass for brubaker run eight minerals are involved in weathering the five primary minerals are ree rich epidote ankerite almandine spessartine garnet muscovite chlorite and the three secondary products are weathered muscovite kaolinite and gibbsite the long term average weathering rates of these minerals were calculated using the six major cations and two trace elements selected from rb sr ba la pr nd sm gd and dy despite having the eight equations needed geochemically reasonable weathering rates e g positive primary mineral rates that reflect destruction could not be achieved regardless of the two trace elements used in the mass balance calculations for brubaker run this is primarily attributable to the natural heterogeneity of the trace element concentrations within the host mineral grains with trace element stoichiometries in some minerals varying by as much as an order of magnitude because the trace elements are hosted by a relatively small number of minerals the computed weathering rates of other minerals become very sensitive to small variations in trace cation stoichiometry ree rich epidote garnet and ankerite within the brubaker run watershed together host nearly all of the ca in the bedrock and completely dissolve at or near the weathering front consequently approximately all of the ca in bedrock is lost from the regolith in bedrock the mole percentages of ca hosted by ree rich epidote garnet and ankerite are 49 mol 4 mol and 43 mol respectively and are determined by the modal abundance of the mineral in the bedrock and its ca stoichiometry the weathering rates of ree rich epidote garnet and ankerite can be determined by distributing to each mineral that fraction of the total watershed ca flux loss for which it is responsible based on its mole percent ca in bedrock by using a base cation that is completely lost from the regolith and knowing the mole percentage of that element in the mineral s undergoing weathering additional equations may be added to the mass balance matrix we term this technique the flux distribution method the flux distribution method eliminates the need for additional equations established using trace elements based on the mineral weathering rates for the brubaker run watershed determined using the flux distribution method the rates at which the weathering front penetrated the bedrock the saprolitization rate are 4 5 m myr 1 and 6 5 m myr 1 for chlorite and muscovite respectively these measured long term average saprolitization rates compare very favorably with published theoretical values for the nearby northern maryland piedmont which range from 2 2 to 5 3 m myr 1

stratigraphy and sedimentology of the great oolite group in the humbly grove oilfield hampshire abstract the main reservoir of the humbly grove oilfield comprises variably dolomitic grainstones and packstones representing the bathonian great oolite group the bathonian sequence commences in lower fuller s earth claystones which coarsen upwards into oncolitic claystones and skeletal packstones probably equivalent to the fuller s earth rock above is a variable succession of wackestones and thin packstones which have a distinctive sandstone at their base this sequence is named here the hester s copse formation the succeeding great oolite limestone is predominantly oolitic and cross bedded on a variety of scales it exhibits both coarsening and fining sequences which have locally well developed capping hardgrounds and burrowed horizons the great oolite limestone is subdivided into three members the lowest the humbly grove member and the highest the herriard member begin with massive shoal oolite deposition but each then pass upward into more interbedded sequences representing a more transgressive environment the middle member the hoddington is a thin but widely correlatable wackestone the overlying forest marble commences abruptly in claystones but there is an upward increase in both the incidence and thickness of discrete oolitic limestones both the great oolite limestone and forest marble were affected by early fresh water dissolution and cementation in addition to the localized development of submarine cements the top of the great oolite group is represented by the cornbrash the lower cornbrash is a thin micritic limestone while the upper cornbrash is a calcareous claystone which passes upwards into the kellaways clay the bathonian sequence overlies the dolomitic limestones of the inferior oolite the lower fuller s earth claystones being interpreted as a basinal marine mudstone sequence marking a substantial deepening and transgressive phase at the opening of the bathonian these mudstones shoal upwards into the quiet but photic water deposits of the fuller s earth rock the hester s copse formation represents the temporary development of wave dominated terrigenous shoreface and lagoonal conditions renewed transgression established a high energy tide dominated carbonate shelf upon which the great oolite limestone was deposited as a series of shoal oolites channels tidal deltas and spill overs periodic exposure of the carbonate sand bodies led to the production of early dissolutional and cementation fabrics that post date and largely obliterate submarine cements the forest marble opened with a further phase of deepening and the temporary establishment of muddy facies subsequently discrete tide dominated ridges and linear channelized oolitic sands prograded into the area the latest bathonian is marked by subsidence of the carbonate ramp to the south of the london platform the cornbrash kellaways clay sequence accumulating under progressively deepening waters

chemical weathering rates of a soil chronosequence on granitic alluvium iii hydrochemical evolution and contemporary solute fluxes and rates although long term changes in solid state compositions of soil chronosequences have been extensively investigated this study presents the first detailed description of the concurrent hydrochemical evolution and contemporary weathering rates in such sequences the most direct linkage between weathering and hydrology over 3 million years of soil development in the merced chronosequence in central california relates decreasing permeability and increasing hydrologic heterogeneity to the development of secondary argillic horizons and silica duripans in a highly permeable younger soil 40 kyr old pore water solutes reflect seasonal to decadal scale variations in rainfall and evapotranspiration et this climate signal is strongly damped in less permeable older soils 250 to 600 kyr old where solutes increasingly reflect weathering inputs modified by heterogeneous flow elemental balances in the soils are described in terms of solid state exchange and pore water reservoirs and input output fluxes from precipitation et biomass solute discharge and weathering solute mineral nutrients are strongly dependent on biomass variations as evidenced by an apparent negative k weathering flux reflecting aggradation by grassland plants the ratios of solute na to other base cations progressively increase with soil age discharge fluxes of na and si when integrated over geologic time are comparable to solid state mass losses in the soils implying similar past weathering conditions similarities in solute and sorbed ca mg ratios reflect short term equilibrium with the exchange reservoir long term consistency in solute ratios when contrasted against progressive decreases in solid state ca mg requires an additional ca source probably from dry deposition amorphous silica precipitates from thermodynamically saturated pore waters during periods of high evapotranspiration and result in the formation of duripans in the oldest soils the degree of feldspar and secondary gibbsite and kaolinite saturation varies both spatially and temporally due to the seasonality of plant respired co2 and a decrease in organically complexed al in deeper pore waters k feldspar is in equilibrium and plagioclase is about an order of magnitude undersaturated hydrologic heterogeneity produces a range of weathering gradients that are constrained by solute distributions and matrix and macropore flow regimes plagioclase weathering rates based on precipitation corrected na gradients vary between 3 and 7 10 16 mol m 2 s 1 these rates are similar to previously determined solid state rates but are several orders of magnitude slower than for experimental plagioclase dissolution indicating strong inhibitions to natural weathering partly due to near equilibrium weathering reactions

tertiary structures and hydrocarbon entrapment in the weald basin of southern england abstract the weald basin of southeast england was formed by rapid subsidence associated with thermal relaxation following early mesozoic extensional block faulting the basin appears initially to have taken the form of an easterly extension of the wessex basin but became the major depocentre during the upper jurassic and lower cretaceous with associated active faulting these movements appear to have ceased prior to albian times and a full upper cretaceous cover is believed to have been deposited in a gentle downwarp which extended far beyond the confines of the weald and wessex basins major inversion of the weald basin took place in the tertiary with both gentle regional uplift which in the eastern part of the basin is estimated to have exceeded 5000 feet 1525 metres and intense local uplift along pre existing zones of weakness which led to the formation of compressional features such as tight folds and reverse faults zones of tertiary deformation appear to have been strongly influenced by underlying particularly hercynian structural trends lower jurassic source rocks reached maturity in the early cretaceous and initial migration occurred at this time often over long distances into traps closed by pre aptian faults tertiary tilting and uplift led to the breaching of many of these pre existing traps and the formation of large folded closures a second phase of hydrocarbon migration particularly of gas took place at this time with significant vertical migration along fault zones major reservoirs located to date occur in middle jurassic carbonates and upper jurassic sandstones but deep burial in the basin has caused considerable destruction of primary reservoir characteristics changes in the temperature and pressure regimes and the mobilization of fluids within the basin resulting from the tertiary uplift caused further diagenetic changes particularly in the carbonate reservoirs exploration of the weald basin remains at a very early stage with a low drilling density to date the more recent drilling has focussed on earlier structures but traps formed or modified during the tertiary movements represent important exploration objectives although general deterioration in reservoir quality towards the centre and east of the basin makes large fold closures in these areas less attractive

solute geochemical mass balances and mineral weathering rates in small watersheds ii biomass nutrient uptake more equations in more unknowns and land use land cover effects abstract paired watersheds are used to develop a deciduous nutrient uptake stoichiometry the watersheds are those of the house rock run and the brubaker run located in the pennsylvania appalachian piedmont usa these two watersheds are nearly identical with respect to bedrock regolith climate geomorphology morphometry baseflow hydrology and type and successional stage of forest vegetation they only differ by the percentage of deciduous forest cover with house rock run having 59 and brubaker run having 76 from differences in their stream chemistries the biomass nutrient uptake stoichiometry of k1 0mg1 0ca1 4 was determined this stoichiometry applies to an aggrading deciduous biomass and differs from those previously used which were derived from net primary production npp data the difference may reflect that macronutrients in plant tissue may also originate from atmospheric inputs and or decomposing biomass although this stoichiometry may not be applied to all deciduous forest covered watersheds it is likely an improvement over a stoichiometry determined from npp data mass balance calculations of mineral weathering rates often suffer from the number of unknowns exceeding the number of equations to add equations to the mass balance matrices two methods are introduced the first method employs zr normalized bulk chemical compositions of bedrock and soil to calculate a mass transfer coefficient for chemical weathering the second approach uses chemical formulae and modal abundances of primary minerals undergoing complete dissolution during weathering both methods allow for calculation of weathering rate constraints without biomass and cation exchange influences these constraints serve as additional equations in the mass balance matrix this study finds that the watershed with the higher percentage of recently abandoned agricultural fields previously used for growing row crops has the higher chemical weathering rate the higher chemical weathering rate reflects greater runoff resulting from reduced evapotranspiration

the role of disseminated calcite in the chemical weathering of granitoid rocks accessory calcite present at concentrations between 300 and 3000 mg kg 1 occurs in fresh granitoid rocks sampled from the merced watershed in yosemite national park ca usa loch vale in rocky mountain national park co usa the panola watershed ga usa and the rio icacos puerto rico calcite occurs as fillings in microfractures as disseminated grains within the silicate matrix and as replacement of calcic cores in plagioclase flow through column experiments using de ionized water saturated with 0 05 atm co2 produced effluents from the fresh granitoid rocks that were dominated by ca and bicarbonate and thermodynamically saturated with calcite during reactions up to 1 7 yr calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates principally biotite mass balance calculations indicate that most calcite had been removed during this time and accounted for 57 98 of the total ca released from these rocks experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution the lack of excess ca and alkalinity indicated that calcite had been previously removed by natural weathering the extent of ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks high ca na ratios relative to plagioclase stoichiometries indicate excess ca in the yosemite loch vale and other alpine watersheds in the sierra nevada and rocky mountains of the western united states this ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains in contrast ca na flux ratios are comparable to or less than the ca na ratios for plagioclase in the subtropical panola and tropical rio icacos watersheds in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport limited weathering these results indicate that the weathering of accessory calcite may strongly influence ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces

initial stages of weathering and soil formation in the morteratsch proglacial area upper engadine switzerland investigations in alpine soils indicate that mineral weathering is much faster in young soils 1000 yr than in old soils 10 000 yr however little is known about the initial stages of weathering and soil formation i e during the first decades of soil genesis in this study we investigated rock forming minerals weathering at very early stages of soil formation due to the continuous retreat of the morteratsch glacier upper engadine swiss alps the proglacial area offers a full time sequence from 0 to 150 yr old surfaces a low slope and the absence of glacier which might have interrupted soil formation processes contributed to the choice of the morteratsch proglacial valley for this case study the area is well documented regarding vegetation and soils the tectonic unit is the bernina crystalline which is mainly constituted of granitoid rocks consequently the glacial till has an acidic character mineralogical measurements were carried out on the soil fraction 2 mm using xrd and drift for qualitative and quantitative phase analysis in addition chemical analyses of the stream water from the main channel tributaries and of rainwater were performed with a special focus on ca sr and sr isotope ratios 87sr 86sr furthermore the accumulation of organic matter within the time sequence and physical soil properties were measured decreasing grain size with time shows active physical weathering processes soil organic matter has been accumulated during 150 yr at very high rates special emphasis has been given to chemical weathering and to the formation and transformation mechanisms of minerals of special interest were biotite chlorite epidote plagioclase and calcite biotite has been continuously transformed into illite like components within 150 yr the concentration of epidote significantly decreased the high ca sr as well as 87sr 86sr ratios in the stream and spring waters confirmed that ca bearing minerals are weathering and transforming at very high rates in the proglacial area also in cryic ice free environments chemical weathering rates are high leading to the formation and transformation of minerals disseminated calcite in granitoid rocks not confined to sedimentary carbonate rocks also plays a role in subglacial environments it is however not known for how long such an influence is significant and measurable the high ca na and ca sr ratio in the stream and tributary waters showed that calcite contributes to the supply of soluble ca although the ion activity product calculations clearly demonstrated that the waters were undersaturated with respect to this mineral

mechanisms for chemostatic behavior in catchments implications for co2 consumption by mineral weathering a r t i c l e i n f o article history concentrations of weathering products in streams often show relatively little variation compared to changes in discharge both at event and annual scales in this study several hypothesized mechanisms for this chemostatic behavior were evaluated and the potential for those mechanisms to in uence relations between climate weathering uxes and co2 consumption via mineral weathering was assessed data from loch vale an alpine catchment in the colorado rocky mountains indicates that cation exchange and seasonal precipitation and dissolution of amorphous or poorly crystalline aluminosilicates are important processes that help regulate solute concentrations in the stream however those processes have no direct effect on co2 consumption in catchments hydrograph separation analyses indicate that old water stored in the subsurface over the winter accounts for about one quarter of annual stream ow and almost one half of annual uxes of na and sio2 in the stream thus ushing of old water by new water snowmelt is an important component of chemostatic behavior hydrologic ushing of subsurface materials further induces chemostatic behavior by reducing mineral saturation indices and increasing reactive mineral surface area which stimulate mineral weathering rates co2 consumption by carbonic acid mediated mineral weathering was quanti ed using mass balance calculations results indicated that silicate mineral weathering was responsible for approximately two thirds of annual co2 consumption and carbonate weathering was responsible for the remaining one third co2 consumption was strongly dependent on annual precipitation and temperature these relations were captured in a simple statistical model that accounted for 71 of the annual variation in co2 consumption via mineral weathering in loch vale published by elsevier b v

dynamics and inversion of the mesozoic basin of the weald boulonnais area role of basement reactivation abstract the geometry and dynamics of the mesozoic basins of the weald boulonnais area have been controlled by the distribution of preexisting variscan structures the emergent variscan frontal thrust faults are predominantly e w oriented in southern england while in northern france they have a largely nw se orientation extension related to tethyan and atlantic opening has reactivated these faults and generated new faults that together have conditioned the resultant mesozoic basin geometries jurassic to cretaceous n s extension gave the weald boulonnais basin an asymmetric geometry with the greatest subsidence located along its nw margin late cretaceous palaeogene n s oriented alpine s l compression inverted the basin and produced an e w symmetrical anticline associated with many subsidiary anticlines or monoclines and reverse faults in the boulonnais extensional and contractional faults that controlled sedimentation and inversion of the mesozoic basin are examined in the light of new field and reprocessed gravity data to establish possible controls exerted by preexisting variscan structures

comparison of episodic acidification of mid atlantic upland and coastal plain streams episodic acidification was examined in five mid atlantic watersheds representing three physiographic provinces coastal plain valley and ridge and blue ridge each of the watersheds receives a similar loading of atmospheric pollutants so42 and no3 and is underlain by different bedrock type the purpose of this research was to quantify and compare the episodic variability in storm flow chemistry in reedy creek virginia coastal plain mill run and shelter run virginia valley and ridge and fishing creek tributary and hunting creek maryland blue ridge because episodic responses were similar from storm to storm in each of the watersheds a representative storm from each watershed was discussed acidification defined as the loss of acid neutralizing capacity anc was observed in all streams except mill run mill run chemistry showed little episodic variability during storms in the other streams ph decreased while so42 no3 and k concentrations increased concentrations of mg2 and ca2 increased in reedy creek and fishing creek tributary but decreased in shelter run and hunting creek therefore the net effect of episodic changes on the acid base status differed among the streams in general greater losses of anc were observed during storms at shelter run and hunting creek watersheds underlain by reactive bedrock carbonate metabasalt comparatively smaller losses in anc were observed at reedy creek and fishing creek tributary watersheds underlain by quartzites and unconsolidated quartz sands and cobbles increased so42 concentrations were most important during storms at reedy creek and fishing creek tributary but organic anions inferred by anion deficit were also a factor in causing the loss of anc dilution of base cations was the most important factor in the loss of anc at shelter run both increased sulfate and dilution of base flow were important in causing the episodic acidification at hunting creek the role of so42 in contributing to episodic acidification in these watersheds is similar to that documented in studies conducted in other regions of the united states scandinavia canada and the united kingdom the importance of so42 in mid atlantic united states streams contrasts with northeastern united states streams in which increased no3 derived from snowpack is more important in causing episodic acidification results support the importance of shallow subsurface processes in determining storm flow chemistry regional climatic characteristics in determining the different sources of acidity during episodes and the importance of bedrock geology in determining the amount of anc loss

petroleum geochemistry of the lower and middle jurassic in atlantic margin basins of ireland and the uk potential hydrocarbon source rocks of lower and middle jurassic age have been reported from outcrop shallow boreholes and exploration wells in atlantic margin basins of the uk hebrides west of shetlands and flanking the ne rockall trough and recently in the continuation of this trend offshore ireland slyne erris and porcupine basins previously these organic rich mudrocks were considered to be of little economic importance due largely to their perceived limited areal distribution and low maturity however recent geochemical studies of oils and shales from exploration drilling of these basins shows the lower and middle jurassic to have considerable potential as effective hydrocarbon source rocks supplanting the late jurassic early cretaceous kimmeridge clay formation equivalents as the only viable oil source rock in the region flanking the atlantic margin in the irish and uk sectors rich oil source potential occurs in two transgressive mudrock cycles of lower jurassic age these are the sinemurian pliensbachian interval and the overlying toarcian section present in basins such as the solan minch hebrides slyne north celtic sea st george s channel and central english channel the middle jurassic source rocks have a more limited areal distribution and occur in the faroe shetland solan west lewis west flannan hebrides slyne and north porcupine basins with oil source potential in regressive marginal marine to lacustrine facies mudrocks geochemical studies were undertaken on mudrocks from the lower and middle jurassic sections in atlantic margin basins outcrop shallow borehole core and exploration well cores and cuttings samples and on oils from drill stem test and shows core and cuttings extracts detailed analyses using gc gc ms and carbon isotopes allowed both characterization of the source rocks and oil to source correlation biomarker and carbon isotope studies of oils from the faroe shetland basin foinaven and schiehallion fields the porcupine basin connemara accumulation the wessex basin wytch farm and kimmeridge oil fields and wells in the slyne basin show strong correlations to the various source rock developments in the lower and middle jurassic the mixed biodegraded foinaven and schiehallion oils have a major waxy component and correlate with lacustrine middle jurassic source rocks in the solan and west lewis west flannan basins middle jurassic sourcing of the connemara oils is also suggested while oils in the slyne basin appear to have been largely sourced by the lower jurassic pabba shale formation oils in the wessex basin wytch farm and kimmeridge appear to have been sourced by hettangian sinemurian mudrocks and those in the north celtic sea basin by toarcian source rocks the results from this study in combination with previously published data show that rich effective oil prone source rocks occur in both the lower and middle jurassic of the atlantic margin basins offshore ireland and the uk these source rocks can be correlated with indigenous oils indicating the existence of a previously under evaluated petroleum system

tectonic evolution of the intra uplift vigodi gugriana khirasra netra fault system in the seismically active kachchh rift basin india implications for the western continental margin of the indian plate abstract the e w striking kachchh rift basin krb at the western continental margin of indian plate is located in the northern part of gujarat state india krb has undergone polyphase deformation owing to changing stress field since late triassic we establish the kinematic framework along the nw striking intra uplift vigodi gugriana khirasra netra fault system vgknfs located at the western part of the krb the vgknfs consists of 0 25 50 km long sub parallel striated reactivated dip slip faults a total of 1150 fault slip data consisting of fault planes and striations attitude were recorded from 66 sites including a single site with systematic joints slip sense of faults was determined by documenting kinematic indicators paleostress analysis was carried out using win tensor t tecto faultkin and sg2ps to compare and validate the results the chi square statistical analysis was undertaken to evaluate how relevant are paleostress analysis results to the present day compressional stress field geophysical investigations were conducted at selected sites using ground penetrating radar gpr to understand the shallow subsurface geometry and trace the continuity of faults buried below patchy alluvial cover 15 17 m long 2d gpr cross sections were recorded across faults using monostatic antenna of 200 mhz frequency two major deformation events d1 and d2 are determined in the present study the extension event d1 shows w and nw nnw extension during late triassic to late cretaceous it occurred during the rift phase of krb in response of the break up of gondwanaland the latest event d2 shows nne ne compression from late cretaceous up to the present it is interpreted to have developed during post rift inversion phase induced by collision of the indian plate with the eurasian plate at 55 ma

cenozoic exhumation of the southern british isles rocks that crop out across southern britain were exhumed from depths of as much as 2 5 km during cenozoic time this has been widely attributed to paleocene regional uplift resulting from igneous underplating related to the iceland mantle plume our compilation of paleothermal and compaction data reveals spatial and temporal patterns of exhumation showing little correspondence with the postulated influence of underplating instead being dominated by kilometer scale variations across cenozoic compressional structures which in several basins are demonstrably of neogene age we propose that crustal compression due to plate boundary forces transmitted into the plate interior was the major cause of cenozoic uplift in southern britain witnessing a high strength crust in western europe

the context of lowstand events in the kimmeridgian late jurassic sequence stratigraphic evolution of the wessex weald basin southern england abstract a depositional sequence stratigraphic framework for the kimmeridgian stage of the wessex weald basin southern england is applied in the investigation of the sedimentary and erosional response to proposed lowstand events this framework recognises 13 sequence boundaries km1 km13 and is based on the integrated assessment of geophysical sedimentological palaeontological and geochemical data changes in the nature and continuity of kimmeridgian unconformity surfaces record the effect of the reorganisation of the onshore basins in response to eustasy and tectonic movements during the earliest kimmeridgian the basin geometry was such that falls in relative sea level generated widespread unconformities associated lowstand events are recorded in marginal areas by a number of sand units derived from a variety of local sources a tectonically enhanced deepening event during the late early kimmeridgian eudoxus zone led to unconformities being confined in their distribution to the basin margins as sea level fell during the latest kimmeridgian a progressive reduction in the depositional area led to an amplification of the effects of lowstand processes at the basin margins where unconformity surfaces are amalgamated on the most positive areas these surfaces are overprinted by a major interregional hiatus the late cimmerian unconformity the timing and effects of kimmeridgian lowstand events were intimately linked to the tectonic evolution of the wessex weald basin thus at times when rates and amounts of eustatic change are small i e during greenhouse times the tectonic signature of a basin will be the primary signal recorded in sedimentary successions

oyster patch reefs as indicators of fossil hydrocarbon seeps induced by synsedimentary faults abstract the late jurassic deposits of the boulonnais area n france represent the proximal lateral equivalent of the kimmeridge clay formation they accumulated on a clastic dominated ramp subject to synsedimentary faulting as a result of the atlantic ocean rifting in the gris nez cape area i e close to the northern border fault zone of the jurassic basin the late jurassic sequence contains small dimensioned oyster patch reefs nanogyra nana embedded in a microsparitic calcite matrix 13 c measurements carried out within both the matrix and the shells display significantly lower values in the matrix compared to the oyster shells which suggests that the carbonate matrix precipitation was involving a carbon source different from marine dissolved inorganic carbon most probably related to sulfate reduction which is evidenced by light 34 s in pyrites similarities but also differences with lucinid rich bioconstructions namely the late jurassic pseudo bioherms of beauvoisin se france suggest that the patch reefs developed at hydrocarbon seeps are related to synsedimentary faults the extensional block faulting segmentation of the northern margin of the boulonnais basin in late jurassic times is thus believed to have induced a sort of small dimension hydrocarbon seepage field recorded by the patch reef distribution

strong tectonic and weak climatic control of long term chemical weathering rates the relationships among climate physical erosion and chemical weathering have remained uncertain because long term chemical weathering rates have been difficult to measure here we show that long term chemical weathering rates can be measured by combining physical erosion rates inferred from cosmogenic nuclides with dissolution losses inferred from the rock to soil enrichment of insoluble elements we used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate implying that by regulating erosion rates tectonic uplift may significantly accelerate chemical weathering rates in granitic landscapes

silicate weathering rate and its controlling factors a study from small granitic watersheds in the jiuhua mountains abstract silicate weathering is intimately linked to global climate to investigate the controlling factors of silicate weathering rate we collected monthly or half monthly river water samples from ten small granitic watersheds in the jiuhua mountains mass balance calculation shows that agricultural activity atmospheric input silicate weathering carbonate weathering and evaporite dissolution contribute 2 0 16 9 58 7 13 5 and 8 9 cations to the river water respectively the disproportionate contribution of carbonate rocks with an exposed area of there is no correlation between silicate weathering rates swr and the suspended solid concentrations an index of physical erosion rate but there is a strong positive correlation between swr and temperature consistent with the kinetic limited chemical weathering regime in alpine areas a compilation of literature data from global small granitic watersheds in different climatic zones shows positive correlations between temperature runoff and swr a multiple linear regression between swr temperature and runoff yielded an adjusted r squared of 0 61 showing that climatic factors can account for 61 of the variation in swr in addition for catchments where the elevation difference between the highest point of the headwater and sampling point an approximate topographical parameter exceeds 400 m the r squared value obtained from the temperature and swr regression analysis is significantly increased indicating that temperature is likely the most important factor controlling silicate weathering in the alpine region where a kinetic limited regime dominates

the nature of the variscan basement in southeast england evidence from integrated potential field modelling the variscides of southeast england are buried beneath post carboniferous cover interpretations of the basement are based mainly on deep boreholes geophysical signatures from the basement are contained within the regional gravity and magnetic data a gravity stripping exercise has been undertaken to remove the gravitational effect of the post variscan cover to generate a residual gravity map this map is interpreted along with integrated potential field modelling along four long interconnected profiles and compared with a revised pre permian subcrop map the magnetic evidence suggests that precambrian magnetic basement of the midlands microcraton has been buried southwards by north vergent variscan thusting over the foreland north of the variscan front short wavelength anomalies superimposed upon this deep precambrian source are due to shallower silurian and carboniferous volcanic rocks many residual gravity lows within the rhenohercynian zone may be related to thick low density devonian basins in the english channel a change in geophysical signature occurs north of the portland wight fault coinciding with phyllites in the basement models are presented in which the english channel magnetic anomalies originate within the pre permian basement comparisons with anomalies in the southwestern approaches suggest that the portland wight thrust is a terrane boundary possibly a subduction related suture implying southerly directed variscan subduction

effects of silicate weathering on water chemistry in forested upland felsic terrane of the usa the authors use data from the us epa national surface water survey nsws the usgs bench mark station monitoring program and the national acid deposition program nadp to evaluate the role of weathering in supplying base cations to surface waters in forested upland felsic terrane of the northeastern northcentral and northwestern idaho batholith us multivariate regression reveals differential effects of discharge on individual base cations and silica but no secular trend in the ca na denudation rate over 24 yr 1965 1988 for the wild river catchment in the white mountains because the turn over time for na in the soil exchange complex is only ca 1 5 yr the long term behavior of the ratios ca na and si na in waters leaving this catchment indicates that weathering is compensating for base cation export in every subregion ca and mg concentrations in lakes are statistically linked to nonmarine na but the median ca na ratio is greater than the ratio in local plagioclase the authors attribute this inequality to nonstoichiometric weathering of calcium in juvenile formerly glaciated terrane not to leaching of exchangeable cations by so sub 4 because intraregional and cross regional statistical analysis reveals no effect of atmospherically derived sulfate ion the median base cation denudation rates meq m supmore minus 2 yr sup minus 1 for these american lake regions are maine granites 108 western adirondack felsic gneiss 85 vermilion batholith 42 idaho batholith 52 the regional rates are high enough to compensate for present wet deposition of acidifying anions except in some vulnerable lake watersheds in the western adirondacks less

recognition of tectonic events in undeformed regions contrasting results from the midland platform and east midlands shelf central england apatite fission track and vitrinite reflectance data from central england demonstrate how these techniques can reveal otherwise unrecognized tectonic and or palaeothermal episodes in apparently tectonically stable areas the results document the transition from an inverted basinal region in the north east midlands shelf to a tectonically stable platform in the south midland platform afta data from the region reveal two discrete cooling episodes in the early and late tertiary maximum palaeotemperatures from afta and vr data in outcrop samples define a consistent increase from 50 c in lower cretaceous and upper jurassic units in the se to around 80 90 c in triassic and older units in the nw these early tertiary palaeotemperatures reflect a combination of deeper burial and elevated basal heat flow results from the rufford 1 well define an early tertiary palaeogeothermal gradient of 40 5 c km 1 32 50 c km 1 at 95 confidence limits corresponding to deeper burial by 1450 m of additional section 1 1 2 2 km at 95 confidence limits subsequently removed by tertiary erosion in contrast geological considerations suggest a maximum overburden of 800 900 m above the base of the lower jurassic in the vicinity of rugby where palaeotemperatures at outcrop are similar to those near the rufford 1 location the discrepancy between stratigraphic and palaeo thermal reconstruction of former burial depths often noted in earlier studies remains unresolved the late tertiary episode is much less well constrained but results from rufford 1 may require between 910 and 1650 m of eroded section thus much of the total amount of removed overburden may have been removed during the late tertiary results from the apley barn borehole oxfordshire reveal a late tertiary palaeothermal episode characterized by a highly non linear palaeotemperature profile which probably reflects local heating due to passage of hot fluids despite stratigraphic evidence for some early tertiary erosion results from this borehole show no evidence of early tertiary effects major early and late tertiary exhumation was limited to regions underlain by older palaeozoic basins while regions overlying palaeozoic basement were more stable experiencing significantly less exhumation we suggest this reflects the preferential reactivation of the weaker basinal regions as a result of compressional events at plate margins our results emphasize the importance of incorporating results from both inverted and non inverted areas in understanding the causal mechanisms of uplift and inversion and highlight the importance of testing apparent stability using palaeo thermal methods