biogenic sedimentation and geochemical properties of deep sea sediments of the demerara slope abyssal plain influence of the amazon river plume abstract the amazon river plume has a major impact on sedimentation at abyssal depths throughout a broad area 450 000 km2 and far 500 1000 km from the river mouth as the plume mixes into the north atlantic ocean it may support ecological niches favorable for n2 fixation driven by the symbiosis between diatoms and diazotrophic cyanobacteria this proposed diatom diazotroph association dda should result in increased carbon export from a limited region of plume influence here we used 32 multicores collected throughout the demerara abyssal slope and plain at depths ranging from 3000 to 5000m to assess patterns and rates of export and accumulation of organic carbon corg or poc and biogenic sio2 bsi sediment accumulation rates were determined from 14c ages of foraminifera obtained at 2 5 depths from 9 cores and were further constrained by 230th measurements the sedimentation rate 1 5 cm ky 1 representing the average accumulation over the past 8000 years was combined with corg and bsi sediment concentrations to establish biogenic matter burial fluxes burial of poc represents 4 16 of the corg raining to the deep sea floor which is high for water depths 4000 m burial of bsi represents 1 9 of the total bsi rain clastic sedimentation dominates regions underlying the plume while carbonate sedimentation dominated otherwise sediment mixing bioturbation was studied in 13 cores using 210pb as a tracer and showed no spatial patterns diffusional mixing coefficients ranged from 0 03 to 3 2 cm year 1 values consistent with other deep sea mixing rates however sites with the highest mixing rates did not have the highest corg content sediment focusing was studied in at 7 sites using 230th as a tracer surficial sediments had focusing factors that ranged from 1 to 2 indicating little sediment redistribution biogenic sedimentation in general and bsi deposition in particular is not concentrated in the region of dda abundance the nw axis of primary plume trajectory is coincident with the maximum deposition and burial of poc and bsi but not caco3

transversal and oblique structures at the serres de llevant thrust belt mallorca island the serres de llevant thrust and fold segment outcrops along the se coast of mallorca balearic isles spain and represents the eastern continuation of the external zones of the alpine betic range the structure of the serres de llevant consists mainly of northwest directed thrusts which involve a sedimentary series ranging in age from upper triassic to middle miocene the thrusts form a thrust system developed both by piggy back and out of sequence thrusting thrust sheets are imbricated to the se and to the sw and in the northern part also to the ne giving rise to a complex 3 d pattern the thrusts and related folds developed during the oligocene and the lower and middle miocene the thrust transport direction has been inferred from the stratigraphic facing directions of all mapped ramps and has been determined with the aid of other transversal structures the resulting transport direction is from se to nw n310e one of the most significant structural features of the serres de llevant thrust segment is the existence of several lateral and oblique structures these structures are ramps which display stratigraphic facing directions both to the ne and sw other lateral structures represented in the northern part of the thrust segment are tear and drop faults in the southern part kilometric scale oblique folds are exposed

calcite dissolution in sediments of the ceara rise in situ measurements of porewater o2 ph and co2 aq in situ electrode measurements of porewater oxygen and ph from four sites on the ceara rise in the western tropical atlantic unequivocally demonstrate that calcite dissolution driven by metabolic co2 produced within the sediments is a significant part of the diagenesis of sedimentary calcite dissolving at least 20 of the calcite rain to the seafloor the first ever in situ absorbance based measurements of porewater co2 aq support the dissolution estimates based on models of the observed ph distributions and are incompatible with scenarios excluding metabolic co2 driven dissolution our dissolution estimates are consistent with those estimated by an independent study of porewater calcium and alkalinity profiles martin and sayles 1996 at this location the consistency of these disparate porewater measurements and our ability to interpret them with simple models of respiration and dissolution implies that no special mechanism is required to describe this process the calcite dissolution rate constant in the sediments of the deepest station in this study is significantly higher than determined by in situ studies at other locations values approach those determined by early laboratory measurements the dissolution rate constant here must be at least two orders of magnitude higher than for calcite in sediments on the ontong java plateau based on in situ electrode measurements there hales and emerson 1996 the calcite solubility consistent with these data is not compatible with that consistent with the ontong java data the reason for this difference is currently unresolved but may be due to the high order of the empirical dissolution rate law assumed in this study

tectono sedimentary characteristics of late miocene quaternary extensional basins of the northern apennines italy abstract extensional and compressional regimes exist at the same time in adjacent parts of the northern apennines italy and the former regime succeeded the latter at the same place as the thrust mountain front moved eastward since miocene times numerous extensional basins have developed west of the present mountain divide the westernmost ones formed over attenuated continental crust since late miocene and have been subjected to several subsidence and uplift events with rates of subsidence generally faster than rates of sedimentation they contain continental deposits overlain by gypsum bearing upper miocene marine sequences and siliciclastic marine pliocene deposits these basins were affected by shallow magmatism and are still experiencing high geothermal gradient and late to post magmatic activities such as in the renowned thermal region of larderello to the east closer to the present mountain divide the extensional basins formed later from pliocene to quaternary contain continental fluvial and lacustrine deposits and have not experienced near surface magmatic activities the sedimentary fill architecture of the apennine extensional basins is similar to that of other european american and african extensional or transtensional systems for instance a common characteristic is the prevalence of large alluvial fan deposits at the hanging wall shoulder of half grabens coarser smaller alluvial fans at the footwall shoulder and some fluvial deposits introduced longitudinally unlike the african rifts though the sedimentary facies distribution of extensional basins which developed in active orogenic zones such as in the apennines may be strongly affected by uplifting steep mountain slopes and can have large thick coarse alluvial fans also on the footwall side of the half grabens

duration of and decoupling between carbon isotope excursions during the end triassic mass extinction and central atlantic magmatic province emplacement abstract changes in 13 c carb and 13 c org from marine strata occur globally in association with the end triassic mass extinction and the emplacement of the central atlantic magmatic province camp during the break up of pangea as is typical in deep time the timing and duration of these isotopic excursions has remained elusive hampering attempts to link carbon cycle perturbations to specific processes here we report 13 c carb and 13 c org from late triassic and early jurassic strata near levanto peru where intercalated dated ash beds permit temporal calibration of the carbon isotope record both 13 c carb and 13 c org exhibit a broad positive excursion through the latest triassic into the earliest jurassic the first order positive excursion in 13 c org is interrupted by a negative shift noted in many sections around the world coincident with the extinction horizon our data indicate that the negative excursion lasts 85 25 kyrs longer than inferred by previous studies based on cyclostratigraphy a 260 80 kyr positive 13 c org shift follows during which the first jurassic ammonites appear the overall excursion culminates in a return to pre perturbation carbon isotopic values over the next 1090 70 kyrs via chronologic isotopic and biostratigraphic correlation to other successions we find that 13 c carb and 13 c org return to pre perturbation values as camp volcanism ceases and in association with the recovery of pelagic and benthic biota however the initiation of the carbon isotope excursion at levanto predates the well dated camp sills from north america indicating that camp may have started earlier than thought based on these exposures or that the onset of carbon cycle perturbations was not related to camp

numerical modeling of propagation and overlap of thrust faults with application to the thrust fold belt of central alberta abstract we use two computer programs to analyze the propagation of multiple thrust faults and their influence on the geometry of a thrust belt they use algorithms based on current equations of fault propagation to generate graphical simulations the simulations are used to demonstrate a model of thrust propagation and thrust belt development that fits current knowledge of fault propagation an alternative to the thrust transfer zone model is proposed called thrust overlap zones the computer simulations provide useful information about the generation and behavior of multiple faults the number of faults the positions of their nucleation points and hence their density the rock properties and rate of fault propagation govern the uniformity of the shortening along the thrust belt thus shortening of a thrust belt can be distributed more evenly by means of propagation of a large number of small faults than by a few large faults the final geometry of a large thrust fault on a geological map provides few clues about its origin i e whether it was produced by the coalescence of a series of en echelon thrust faults or from only a single fault a simple kinematic model based on map length and position of known thrust faults imitates the curved fault map patterns of a segment of the thrust fold belt of central alberta

balanced cross sections and their implications for the deep structure of the northwest alps reply abstract the structure of the northwest external french alps around the internal belledonne and mont blanc massifs in the beaufortain area can be explained by foreland wnw propagating thrust tectonics the internal belledonne massif is interpreted as having developed by imbrication of an originally thin skin of basement with a mesozoic cover above this massif all thrusts tend to climb lateral sections to the south to converge with the frontal pennine thrust the southern termination of the mont blanc massif is merely a spectacular example of such a lateral ramp

sr ca mg ca ratios and sr and stable isotopes of biogenic carbonates from the late miocene velona basin central apennines italy provide evidence of unusual non marine messinian conditions abstract the sr ca and mg ca ratios of fossil ostracod and mollusc shells from a late miocene early messinian lacustrine sequence in the velona basin central apennines italy were used to calculate the sr ca and mg ca of waters in which these taxa lived sr ca of these waters were always higher than the sr ca calculated for the messinian seawater despite the broad salinity ranges fresh water oligo mesohaline inferred from the paleontological analyses the estimated mg ca water from the velona samples are below the mg ca value for coeval seawater even though they represent relatively high values when compared with many non marine waters the salinity variations of the velona lacustrine system recorded by changes in faunal assemblages are linked to variable inputs of na cl from deep groundwaters and are not reflected in significant changes in sr ca and mg ca of the waters calculated from shell chemistry the combination of 18 o signatures and sr isotopic ratios from molluscs from the velona basin suggests a non marine environment during some episodes of the lake history given the saline inputs the waters in the lake would attain a large solute concentration oligo to mesohaline although they retained the meteoric 18 o signature we compare the paleohydrochemical inferences from the studied sequence with other messinian records and we show the importance of combining paleoecological and geochemical proxies to obtain consistent paleoenvironmental reconstructions

late cretaceous stratigraphy deformation and intrusion in the madison range of southwestern montana dating of orogenic rock units in the central part of the madison range shows that laramide deformation was virtually completed by the end of the cretaceous early campanian k ar dates of about 79 m y were obtained from welded tuffs in the basal part of the livingston formation a volcanic and volcaniclastic assemblage that is conformable with underlying cretaceous clastic rocks and with the overlying sphinx conglomerate no datable materials were obtained from the sphinx but both it and the livingston were deformed by the hilgard fault system a series of thrust faults and associated folds which extend along the western side of the southern two thirds of the range this north trending fault system represents the culmination of laramide shortening within the range k ar and 40 ar 39 ar dating of hornblende from dacitic laccolithic rocks that intruded the hilgard fault system in the central part of the range indicates an approximate date of 68 69 m y b p for emplacement of the igneous suite the dacite postdates movement along faults of the hilgard fault system and postdates the synorogenic sphinx conglomerate

caco3 dissolution in sediments of the ceara rise western equatorial atlantic we have used porewater sampling by in situ techniques including whole core squeezing as well as by shipboard sectioning and whole core squeezing to estimate the rates of sedimentary organic matter oxidation and caco3 dissolution at seven sites on the ceara rise in the western equatorial atlantic ocean porewater no3 profiles at all sites show a pattern indicative of active organic matter oxidation in the upper 15 20 cm of the sediments and in a buried organic rich layer the organic c oxidation rate generally decreases with increasing water depth from a value of 22 mol cm2 y at the shallowest site 3279 m to 14 mol cm2 y at the deepest site 4675 m over this depth range the bottomwaters vary from moderately supersaturated with respect to calcite to strongly undersaturated high resolution alkalinity profiles measured in porewaters collected by in situ whole core squeezing yield estimated ca2 fluxes of 11 mol cm2 y at a site located at the depth of the calcite saturation horizon and 7 6 zmol cm2 y at a moderately undersaturated site ca2 fluxes calculated from profiles in porewaters collected by relatively coarse resolution in situ sampling methods clearly indicate that there is caco3 dissolution above the calcite saturation horizon the dissolution of aragonite may contribute to the dissolution flux at the shallowest site these ca2 fluxes as well as fluxes estimated from a model of sedimentary organic matter oxidation and calcite dissolution indicate that 36 66 of the caco3 rain to the seafloor dissolves at sites at and above the calcite saturation horizon while 52 75 of the rain dissolves at sites below this depth when these results are incorporated into the oceanic caco3 budget of milliman 1993 they indicate that 35 of caco3 production is preserved in the deep sea they suggest a caco3 accumulation rate that is 27 lower than that estimated by milliman 1993 our corg oxidation caco3 dissolution model indicates that a large fraction of the caco3 dissolution that is occurring on the ceara rise is attributable to the neutralization of metabolic acids produced during organic matter oxidation the efficiency with which organic matter oxidation dissolves caco3 that is the ratio caco3 dissolution attributable to organic matter oxidation organic matter oxidation rate generally increases as degree of undersaturation of bottomwaters increases however there are deviations from the general trend that can be attributed to site to site variations in the kinetics of organic matter oxidation and calcite dissolution this result indicates that the dissolution of caco3 as a result of organic matter oxidation in the deep sea may mask the effects of variations in surface water caco3 productivity and bottomwater chemistry on the accumulation rate of caco3 in deep sea sediments

evidence in support of first order dissolution kinetics of calcite in seawater abstract re examination of an experimental determination of the dissolution rate of reagent grade calcite in seawater shows that the original conclusion of rate law with 4 5 order dependence on undersaturation was very sensitive to uncertainties in the saturation state of the seawater with respect to calcite c in particular use of an erroneously high value of the calcite stoichiometric solubility product generated correspondingly low values of the saturation state extrapolation of the experimental measurements to a rate of zero dissolution indicates that the calcite solubility was about 20 lower than that used in the original study similar to more recent estimates if the lower solubity is used for recalulation of the experimental saturation states the dissolution rate rd c day 1 is adequately described by the rate experssion rd c 38 1 omega c 1 in situ measurements of ph in the pore waters of calcite rich sea floor sediments are more consistent with first order kinetics than with 4 5 order kinetics interpretation of pore water ph data using the 4 5 order rate expression requires dissolution rate constants that are different by at least two orders of magnitude and stoichiometric calcite solubility products that are different by several percent between two otherwise similar sites application of the first order dissolution reduces the variability in the rate constant to less than one order of magnitude and all in situ observations are consistent with a single estimate of calcite solubility first order kinetics do not reduce the discrepancy between the laboratory determined rate constants and those based on pore water measurements dissolution rate constants constrained by the in situ ph measurements are at least two orders of magnitude less than the laboratory results

decadal changes in the aragonite and calcite saturation state of the pacific ocean 1 based on measurements from the woce jgofs global co2 survey the clivar co2 repeat hydrography program and the canadian line p survey we have observed an average decrease of 0 34 yr 1 in the saturation state of surface seawater in the pacific ocean with respect to aragonite and calcite the upward migrations of the aragonite and calcite saturation horizons averaging about 1 to 2 m yr 1 are the direct result of the uptake of anthropogenic co2 by the oceans and regional changes in circulation and biogeochemical processes the shoaling of the saturation horizon is regionally variable with more rapid shoaling in the south pacific where there is a larger uptake of anthropogenic co2 in some locations particularly in the north pacific subtropical gyre and in the california current the decadal changes in circulation can be the dominant factor in controlling the migration of the saturation horizon if co2 emissions continue as projected over the rest of this century the resulting changes in the marine carbonate system would mean that many coral reef systems in the pacific would no longer be able to sustain a sufficiently high rate of calcification to maintain the viability of these ecosystems as a whole and these changes perhaps could seriously impact the thousands of marine species that depend on them for survival

early middle miocene tectonic uplift of the northwestern part of the qinghai tibetan plateau evidenced by geochemical and mineralogical records in the western tarim basin the tarim basin in western china has been receiving continuous marine to lacustrine deposits during the cenozoic as a foreland basin of the qinghai tibetan plateau qtp clay mineralogy and geochemical proxy data from these sedimentary archives can shed light on climate and tectonic trends here we report on an abrupt mineralogical and weathering shift at 17 ma 1 myr in the miocene qimugan section in the northwestern part of the qinghai tibetan plateau the rapid shift involves decreasing trends of chemical weathering indices rb sr and ba sr ratios and of minor and immobile elements with respect to upper crust composition as well as increasing trends of na al and na ti ratios smectite chlorite and calcite contents we ascribe these trends to changing source rocks due to uplift of the northern part of the qtp leading to exposures of younger intrusive bodies and older gneisses schists and carbonate rich rocks these uplifts potentially caused regional aridification reducing chemical weathering the dating is indirect via magnetostratigraphically dated ostracod biostratigraphy and detrital zircon chronology and currently not good enough to compare the shift accurately in time with the onset of the global middle miocene climate optimum mmco at 16 5 ma nevertheless regional tectonics seem to have dominated over global climate as the warmer mmco is expected to have increased weathering indices and decreased na al and na ti rather than the observed reverse trends

centrifuge modelling of thrust faulting structural variation along strike in fold thrust belts abstract the three dimensional geometry and the kinematic evolution of fold thrust structures are investigated by analog modelling using the centrifuge technique we focus on along strike structural variation and transfer of displacement between faults and folds the total horizontal shortening across the model fold thrust belts is constant yet there are systematic variations in shortening by the mechanisms of thrusting folding and layer parallel shortening these along strike changes in structural geometry and strain mechanism are manifestations of displacement transfer the model thrust faults have different amounts of thrust displacement at different points along strike the variation is accommodated by transfer of displacement to over or underlying faults or to en echelon faults by transfer of shortening into folding or by transfer of displacement into layer parallel shortening in the models it is clear that faults nucleate at points that are localized by earlier folding of competent units faults nucleated at different points along a single fold may propagate along the fold and link together to form major thrusts the thrust displacement in such cases varies from smaller values at linkage points to larger values at nucleation points the models have a stratigraphie succession like that of the central appalachian valley and ridge province after an equivalent amount of structural shortening the models exhibit structural features analogous to those of the valley and ridge the lowest competent unit equivalent to the cambro ordovician lithotectonic unit forms a large scale duplex like that of the waynesboro sheet the middle competent unit equivalent to the siluro devonian clastic units forms anticlinoria and synclinoria like those of the martinsburg sheet these structures are spatially associated with underlying culminations and depressions that reflect respectively large and small displacements on thrusts that ramp through the lowest competent unit however in the models it appears that the amplitude of buckling of the middle unit controls the amount of displacement on underlying thrusts whereas in the appalachians the structural culminations of the middle unit are interpreted to have been caused by large displacement on underlying faults

thrust faults and back thrusts in madison range of southwestern montana foreland in the rocky mountain foreland of southwestern montana a zone of late cretaceous thrust faults named the hilgard fault system extends along the west side of the madison range from hebgen lake northward for about 50 mi 80 km the thrust faults are steep at their leading edges but flatten westward beneath the associated plates where they commonly dip 25 30 structural lows and highs are apparent beneath the beaver creek plate the major thrust sheet of the system and correlate with salients and reentrants of the plate the beaver creek plate consists primarily of archean metamorphic rocks but phanerozoic strata are preserved along the northern part of the plate s leading edge only the forward part of the plate is preserved in the madison range because c nozoic normal faults of the madison range fault system dropped much of the plate beneath the madison valley on the west the kirkwood plate lies east of and beneath the beaver creek plate and contains structures of the eastern part of the hilgard system the central segment of the leading edge of the kirkwood plate is not completely detached from underlying strata the leading edge of the northern part of the plate defined by the cache creek fault is flanked on the west by an associated anticline the southern end of the cache creek fault is an eastward dipping back thrust which abruptly steepens on the west adjacent to the anticline both the fault and the anticline are believed to have formed above a concealed detachment fault the southern part of the kirkwood plate displays structures interpreted to represent displacement transfer from the beaver creek plate back thrusts are associated with both thrust plates and played a key role in accommodating strain associated with folding the strata at the leading edges of the plates the back thrusts project upward from the main thrust fault beneath each plate they dip eastward at moderate angles in their lower segments but steepen at structurally higher levels they become overturned locally and dip westward in their uppermost segments the northern part of the study area contains the northwest trending buck creek reverse fault which dips steeply to the northeast movement on this structure ceased before the north trending thrust faults of the hilgard system were emplaced

dynamics of fossil fuel co2 neutralization by marine caco3 a detailed model of the ocean circulation and carbon cycle was coupled to a mechanistic model of caco3 diagenesis in deep sea sediments to simulate the millennium scale response of the oceans to future fossil fuel co2 emissions to the atmosphere and deep sea simulations of deep sea injection of co2 show that caco3 dissolution is sensitive to passage of high co2 waters through the atlantic ocean but caco3 dissolution has a negligible impact on atmospheric pco2 or the atmospheric stabilization co2 emission in the coming centuries the ultimate fate of the fossil fuel co2 will be to react with caco3 on the seafloor and on land an initial caco3 dissolution spike reverses the net sedimentation rate in the ocean until it is attenuated by an enhanced vertical gradient of alkalinity after about 1000 years the magnitude of the initial spike is sensitive to assumptions about the kinetics for caco3 dissolution but subsequent behavior appears to be less model dependent neutralization by seafloor caco3 occurs on a timescale of 5 6 kyr and is limited to at most 60 70 of the fossil fuel release even if the fossil fuel release is smaller than the seafloor erodible inventory of caco3 additional neutralization by terrestrial caco3 restores a balance between caco3 weathering and seafloor accumulation on a timescale of 8 5 kyr while the deficit of seafloor caco3 the lysocline is replenished with an e folding timescale of approximately 18 kyr the final equilibrium with caco3 leaves 7 8 of the fossil fuel co2 remaining in the atmosphere to be neutralized by the silicate rock cycle on a time frame of hundreds of thousands of years

interaction and linkage of extension fractures and normal faults examples from the rift zone of iceland abstract field and photogeological studies were made of 90 zones of interacting fracture segments along the rift zone of iceland each zone consists of a pair of extension fractures or a pair of normal faults with lengths from metres to kilometres these zones evolve from an underlapping stage through an overlapping stage the most common configuration and finally to a linkage stage of all the zones only 7 are underlapping whereas 93 are overlapping with hook shaped fracture pairs the length width ratios of the overlapping zones have a mean value of 3 5 the preferred geometry of the overlapping zones depends upon the initial configuration of the interacting fractures length overstep and the development of the interaction in the overlapping zones most fracture pairs show moderate shear strike slip components related to local variations in the extension opening directions vertical displacements on normal faults decrease as the overstep and length of overlapping zones increase both in turn are proportional to the total lengths of the faults forming the pair the geometrical and kinematic features of overlapping spreading centres at mid ocean ridges show close similarities to those reported here these similarities indicate that the architecture and evolution of overlapping zones are scale independent

selective reverse reactivation of normal faults and deformation around reverse reactivated faults in the mesozoic of the somerset coast abstract normal faults exposed in the triassic jurassic limestones and shales of the somerset coast were formed during the mesozoic development of the bristol channel basin reverse reactivation of some of these normal faults occurred during late cretaceous to early tertiary north south contraction the contraction is also evident from thrusts and conjugate strike slip faults preferential reactivation of the normal faults is attributed to 1 decreased fault plane friction 2 domino block rotation 3 displacement magnitude and 4 fault connectivity the geometries of overlapping and underlapping zones in reactivated fault zones are dependent on the existing structural geometry two distinctive styles of displacement accommodation occur between reverse reactivated normal faults 1 formation of a network of strike slip faults conjugate about nne ssw and 2 oblique steeply dipping reverse faults interaction between strike slip and an existing fault is dependent on whether the normal fault was reactivated the range of structures related to the north south contraction has been incorporated into a single deformation model controlled by the northwards movement of the hanging wall of the quantock s head fault pure dip slip movement occurred in the centre of its curved fault trace with a sinistral component at the western tip and a dextral component of displacement and strike slip block rotations occurred at the eastern tip shortening of these blocks was achieved through development of a strike slip fault network and nw striking thrusts in an underlap zone loading of the footwall by the hanging wall block modified the local stress system to allow formation of oblique steeply dipping reverse faults

comparative ecological analysis of the ostracod faunas from low and high polluted southwestern spanish estuaries a multivariate approach abstract the distribution and abundance of both living and total ostracod populations from the estuaries of the southwestern spanish coast are discussed a total of 68 species were obtained from 120 bottom samples collected in the channels channel margins and salt marshes four assemblages were recognized in this area a urocythereis oblonga assemblage with marine species well represented in sandy substrates located near the mouths b loxoconcha rhomboidea assemblage mainly developed in the quiet tidal channels conected with the main channels of the marine domains c loxoconcha elliptica assemblage enclosing the most cosmopolitan and euryhaline species very abundant in muddy sediments and low to moderate hydrodynamic conditions and d leptocythere porcellanea assemblage only observed in the clayey silty channel margins of the most protected ebb channels in these transitional environments very unfavorable conditions for the ostracod development were found in a the erosional channels and channel margins b most of the salt marsh samples with high subaerial exposure and c sectors with high metallic pollution levels and acidic waters

deformation within foreland thrust sheets by populations of minor faults the dominant deformation mechanism within foreland thrust sheets is the displacement of blocks of weakly deformed rock on discrete mineral coated minor faults in highly deformed layers at the bases of three southern appalachian foreland sheets such minor faults are members of families or populations of consistently oriented structures the deformation style is similar in all three sheets rock nearest each thrust was shortened in the direction of sheet transport and thickened by a family of faults oriented at low angles to the thrusts rock further above each thrust experienced only the first of these two deformation stages statistical analyses of fault populations from these three sheets demonstrate that their deformation is quantitatively as well as qualitatively similar deformation due to movement on minor faults is statistically homogeneous at the scale of an outcrop in one of these sheets strain due to minor faults can be measured in that sheet a strain profile across this sheet is similar to strain profiles across continuously deformed sheets from internal portions of mountain belts suggesting that their responses to emplacement are similar

using laterally compatible cross sections to infer fault growth and linkage models in foreland thrust belts abstract we investigate changes in shortening displacement and fold geometry to understand the detailed along strike structural variation within fold thrust belts and infer thrust growth and linkage mechanisms field observations from the vercors in se france are used to characterise deformation style in the region parallel cross sections are constructed analysed and used to create shortening and thrust displacement profiles from the northern to southern vercors sections show changes in structural style and shortening accommodation from thrust dominated in the north to fold dominated in the south the total shortening distance in the vercors does not change significantly along strike 3400 4650 m however displacements along individual thrust zones do vary significantly and displacement profiles show a range in displacement gradients 16 107 m km despite relatively simple shortening patterns in the vercors sections show a more complex 3d internal structure of the fold thrust belt thrust displacements and geometries suggest both large scale thrust zones and small scale thrusts are soft linked transferring displacement along strike through transfer zones short soft linked thrust segments indicate an intermediate stage of thrust growth and linkage well documented for normal fault systems which form prior to the formation of thrust branches and hard linked displacement transfer

possible overestimation of shallow depth calcium carbonate dissolution in the ocean 1 we argue that diagnostics of excess dissolved calcium carbonate ta above the saturation horizon cannot be unambiguously interpreted in terms of local in situ dissolution we examine a three dimensional numerical model of global ocean circulation and biogeochemistry with explicit representation of the formation and dissolution of calcium carbonate in particular dissolution is only allowed to occur below the saturation horizon the model qualitatively captures the observed basin and global scale patterns of alkalinity and ta as well as the relationship between ta and chlorofluorocarbon age in the thermocline the existence of ta above the saturation horizon in the model can only be explained in terms of transport subsequent to dissolution the model study does not rule out the possibility of shallow depth calcium carbonate dissolution but suggests that dissolution rates derived from tracer observations have not adequately accounted for the influence of transport

a new kinematic evolutionary model for the growth of a duplex an example from the rangit duplex sikkim himalaya india abstract the lesser himalayan duplex lhd is a prominent structure through much of the lesser himalayan fold thrust belt in the darjeeling sikkim himalaya a component of the lhd is exposed in the rangit window as the rangit duplex rd the rd consists of ten horses of the upper lesser himalayan sequence gondwana buxa upper daling the duplex varies from hinterland dipping in the north through an antiformal stack in the middle to foreland dipping in the south the ramgarh thrust rt is the roof thrust and based on a balanced cross section the main himalayan sole thrust is the floor thrust at a depth of 10 km and with a dip of 3 5 n retrodeformation suggests that the rd initiated as a foreland dipping duplex with the early ramgarh thrust as the roof thrust and the rt as the floor thrust the rt became the roof thrust during continued duplexing by a combination of footwall imbrication and concurrent rt reactivation this kinematic history best explains the large translation of the overlying mct sheets the restoration suggests that rd shortening is 125 km and the original gondwana basin extended 142 km northward of its present northernmost exposures within the window

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

modeling the calcite lysocline a numerical model of calcite dissolution in contact with sediment pore water is used to predict the depth and shape of the calcite lysocline in the deep sea model results are compared with lysocline data from 13 regions in the atlantic pacific and indian oceans the model lysocline shape is sensitive to the calcite dissolution rate constant the calcite organic carbon and refractory material rain rates and the rates of oxic versus anoxic organic carbon degradation in the sediment the model is able to reproduce the observed lysocline within the constraints of the sediment trap and calcite accumulation data using a calcite dissolution rate constant of 30 100 d 1 a molar ratio of organic carbon to calcite rain rates of 0 5 1 0 and an initial caco3 fraction of 90 excluding organic carbon this rate constant is consistent with microelectrode results presented by archer et al 1989 the model predicts that 30 50 of the calcite rain to the sea floor at the saturation horizon dissolves in response to organic carbon respiration consistent with previous modeling studies the range in the best fit value of the organic inorganic carbon rain rates arises from model sensitivity to uncertainty in the rate of anoxic carbon degradation in the sediment and in the rain rate of refractory material rather than from scatter in the data lysocline data from the western equatorial atlantic are anomalous to the rest of the data this anomaly may be explained by high rates of refractory material sedimentation from the amazon river

detection and projection of carbonate dissolution in the water column and deep sea sediments due to ocean acidification 1 dissolution of fossil fuel co2 in seawater results in decreasing carbonate ion concentration and lowering of seawater ph with likely negative impacts for many marine organisms we project detectable changes in carbonate dissolution and evaluate their potential to mitigate atmospheric co2 and ocean acidification with a global biogeochemistry model hamocc forced by different co2 emission scenarios our results suggest that as the anthropogenic co2 signal penetrates into ocean interior the saturation state of carbonate minerals will drop drastically with undersaturation extending from the ocean floor up to 100 150 m depth in the next century this will induce massive dissolution of caco3 in the water column as well as the sediment increasing the total alkalinity ta by up to 180 mol kg 1 at the surface and in the ocean interior over the next 2500 years model results indicate an inhomogeneous response among different ocean basins atlantic carbonate chemistry responds faster and starts recovering two millennia after co2 emissions cease which is not the case in the pacific caco3rain stops in the pacific ocean around 2230 using an observation derived detection threshold for ta we project detectable dissolution driven changes only by the year 2070 in the surface ocean and after 2230 and 2500 in the deep atlantic and pacific respectively we show that different model assumptions regarding dissolution and calcification rates have little impact on future projections instead anthropogenic co2 emissions overwhelmingly control the degree of perturbation in ocean chemistry in conclusion ocean carbonate dissolution has insignificant potential in mitigating atmospheric co2 and ocean acidification in the next millennia

a novel determination of calcite dissolution kinetics in seawater we present a novel determination of the dissolution kinetics of inorganic calcite in seawater we dissolved 13 c labeled calcite in unlabeled seawater and traced the evolving 13 c composition of the fluid over time to establish dissolution rates this method provides sensitive determinations of dissolution rate which we couple with tight constraints on both seawater saturation state and surface area of the dissolving minerals we have determined dissolution rates for two different abiotic calcite materials and three different grain sizes near equilibrium dissolution rates are highly nonlinear and are well normalized by geometric surface area giving an empirical dissolution rate dependence on saturation state of rate g cm 2 day 7 2 0 6 10 4 1 3 9 0 1 this result substantiates the non linear response of calcite dissolution to undersaturation the bulk dissolution rate constant calculated here is in excellent agreement with those determined in far from equilibrium and dilute solution experiments plots of dissolution versus undersaturation indicates the presence of at least two dissolution mechanisms implying a criticality in the calcite seawater system finally our new rate determination has implications for modeling of pelagic and seafloor dissolution nonlinear dissolution kinetics in a simple 1 d lysocline model indicate a possible transition from kinetic to diffusive control with increasing water depth and also confirm the importance of respiration driven dissolution in setting the shape of the calcite lysocline

the role of bed parallel slip in the formation of blind thrust faults abstract a finite element code is used to model the mechanical behaviour of elastoplastic sedimentary layers that are deformed by the movement of a faulted deformable basement the propagation of the blind thrust fault is analysed in terms of the evolution of strain localization in the elastoplastic layers of strain softening and strain hardening materials the role of layer thickness bedding parallel slip and fault dip are also studied we found that if no interlayer slip is allowed blind thrusts tend to propagate with constant dip regardless of the rheological properties of the sediment layers however if bedding parallel slip is present a mechanical decoupling appears between layers allowing stress transfers along large distances and favouring the formation of backthrusts fault dip also has significant influence on the qualitative behaviour when interlayer slip is possible a steep fault will tend to split

strains and folds within thrust sheets an analysis of the heilam sheet northwest scotland abstract the changes of shape and orientation of fossil worm burrows have been used to carry out a detailed strain analysis of the heilam thrust sheet in the moine thrust zone northwest scotland the strains have been factorised into components of layer parallel shear 1 layer normal shear 2 and layer parallel shortening or elongation variations in the 1 shear are largely lithologically controlled some strain is due to flexural processes as the thrusts and overlying beds change dip over thrust ramps or are tightened by later deformation while there may also be a component of drag which increases towards the overlying thrust this predating the shear due to flexure a contoured map of the values suggests that major folds within the thrust sheet developed as a result of stick or drag on the floor thrust prior to ramp climb this led to differential movement in the transport direction causing layer parallel shortening accompanied or followed by buckling of the layers a map showing layer normal shear strains 2 suggests that the heilam sheet forms a major surge zone the central part having moved further wnw than the northern and southern parts this has led to components of lateral shear along parts of the sheet especially in the north producing curvature of the imbricate faults

triangle zone and displacement transfer structures in the eastern front ranges southern canadian rocky mountains the geometry of a relict triangle zone at the boundary of the foothills and front ranges in the southern canadian rocky mountains is constrained by detailed surface mapping over 700 m of relief and by seismic reflection data the geometry and progressive development of the triangle zone along a strike length of 15 20 km in the displacement transfer zone between the coleman and misty thrusts is illustrated using closely spaced balanced cross sections palinspastic restorations and a sequentially restored cross section structural geometries show that a northeast foreland verging mainly carbonate wedge of mississippian to triassic rock was inserted along a major upper detachment zone in shale near the base of the jurassic cretaceous clastic package this was accompanied by southwest hinterland verging displacements along the upper detachment zone tectonic thickening of the clastic package exceeding 200 and backthrusting later northeast verging deformation slightly modified the triangle zone by steepening structures tightening folds and minor thrusting recognition of relict triangle zones within the fold and thrust belt may document important changes in the rate of thrust front advancement and aid in the delineation of potential hydrocarbon traps similar to those discovered along th present day thrust belt margin in the southern canadian rocky mountains

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

carbonate dissolution rates at the deep ocean floor 1 this paper reexamines experimental data on the seawater dissolution of caco3 bearing sediment beds to establish that the dependence of the calcite dissolution rate is linearly dependent on the calcite saturation state of the overlying water this linearity is inherent to the original data and is not the result of an error in the solubility product for calcite a comparison between these linear kinetics and the rate of solute transport across the benthic boundary layer further reveals that the overall rate of dissolution at ocean depths below the saturation horizon is controlled by boundary layer transfer a carbonate mass balance model for the sediment water interface which includes both kinetics and boundary layer effects predictively reproduces the currently observed caco3 depth distribution for two test areas in the oceans these findings allow important simplifications in modeling co2 neutralization in the oceans

the rapid resetting of the ca isotopic signatures of calcite at ambient temperature during its congruent dissolution precipitation and at equilibrium abstract this study provides direct experimental evidence of the resetting of the calcium ca isotope signatures of calcite in the presence of an aqueous fluid during its congruent dissolution precipitation and at equilibrium at ambient temperatures over week long timescales batch reactor experiments were performed at 25 c in aqueous nacl solutions air or co2 gas mixtures were bubbled through this fluid to fix ph during congruent calcite dissolution the fluid became enriched in isotopically heavy ca and the ca isotope composition continued to become heavier after the fluid attained bulk chemical equilibrium with the mineral the 44 42ca composition of the fluid was up to 0 8 higher than the dissolving calcite at the end of the dissolution experiments calcite precipitation was provoked by increasing the reactor fluid ph after chemical equilibrium had been attained via dissolution rayleigh isotope fractionation effects were observed immediately after the ph was increased and rapid calcite precipitation occurred however isotopic exchange continued after the system chemically equilibrated eradicating this rayleigh signal taken together these observations 1 confirm dynamic mineral fluid equilibrium i e dissolution and precipitation occur at equal non zero rates at equilibrium and 2 indicate that isotopic compositions of calcite can readily equilibrate even when this mineral is in bulk chemical equilibrium with its coexisting fluid this latter observation suggests the preservation of paleo environmental isotopic signatures in calcite may require a combination of the isolation of the fluid mineral system from external chemical input and or the existence of a yet to be defined calcite dissolution precipitation inhibition mechanism

topological constraints on imbricate thrust networks examples from the mountain city window tennessee u s a abstract the geometry of thrust belts is best described in three dimensions as a network of linear geometric elements trailing branch lines where two thrusts diverge leading branch lines where two thrusts converge tip lines where thrust displacement vanishes and cutoff lines where a stratigraphic horizon intersects a thrust plane there are a number of topological constraints in three dimensions on the interrelationship of these linear elements these constraints provide a method of deciphering the three dimensional structure of an area from the geologic map pattern alone if topography or structural culminations and depressions create significant structural relief the mountain city window tennessee is an example of an imbricate thrust network which reveals its topology on the map pattern because of the presence of culminations the analysis of linear elements in this area allows the regional structural geometry to be described and also two kinematically distinct types of imbricate thrust systems to be characterized namely hinterland and foreland dipping duplexes the doe ridges culmination is a hinterland dipping duplex characterized by leading branch lines in a common roof thrust with the branch lines arranged in the same order hinterland to foreland as in the undeformed state the limestone cove culmination is a foreland dipping duplex characterized by trailing branch lines in a common roof thrust with the branch lines reversed in order hinterland dipping duplexes are the common and well known type foreland dipping duplexes are formed by successive trailing branch lines moving up off the lower flat horizon onto the ramp at which the imbricate slices are formed

magnetostratigraphy of the late miocene baccinello cinigiano basin tuscany italy and the age of oreopithecus bambolii faunal assemblages abstract this study has the aim of dating the latest miocene hominoid oreopithecus bambolii bearing succession of the baccinello cinigiano basin bcb in southern tuscany italy since the 1960s biochronology has been the source for rough age estimations geochronological techniques have started to provide significant time constraints after the absolute dating obtained from a single point in the bcb where a relatively thick and continuous lithostratigraphic record is found together with a succession of several mammal sites chronological control of the sedimentary succession and age range of oreopithecus faunal assemblage has nowadays only been possible with the characterization of the magnetostratigraphy of the bcb sedimentary succession this study demonstrates that i the oldest oreopithecus bearing sediments in bcb v1 has an age older than 8 1 ma ii the igf 4883v oreopithecus from trasubbie creek has an age of 8 1 7 7 ma iii the youngest oreopithecus remains from the so called v2 assemblages have an age between 7 1 and 6 7 ma iv the oreopithecus chronologic range within the bcb is about 1 5 ma long bracketed between 8 3 and 6 7 ma v the post oreopithecus faunal complex v3 bearing deposits likely to have an age between 6 7 and 6 4 ma belonging to the very early mn13 unit early messinian and finally vi oreopithecus is confirmed to be the youngest dryopithecine record from eurasia extending his last occurrence into the early messinian

structure burial history and petroleum potential of frontal thrust belt and adjacent foreland southwest montana the frontal thrust belt in the lima area of southwestern montana consists of blind nonsurfacing thrusts of the lima thrust system beneath the lima anticline and the tendoy thrust sheet to the west the tendoy sheet involves mississippian through cretaceous rocks of the southwest plunging nose of the mesozoic blacktail snowcrest uplift that are thrust higher northeast onto the uplift the front of the tendoy sheet west of lima locally has been warped by later compressive deformation which also involved synorogenic conglomerates of the structurally underlying beaverhead formation to the north recent extension faulting locally has dropped the front of the tendoy sheet beneath quaternary gravels rocks of the exposed tendoy sheet have never been deeply buried based on itrinite reflectance of the laramide blacktail snowcrest uplift east of the frontal thrust belt is asymmetric its southeast steeper limb is exposed along the snowcrest range this limb extends southwestward in the complexly deformed snowcrest structural terrane northwest dipping thrusts on this limb involve basement rocks and probably merge with depth into a major sub snowcrest range thrust this major thrust borders and is chiefly responsible for the blacktail snowcrest uplift and adjacent ruby synclinorium to the southeast uniform conodont cai values of 1 from both the southeast and northwest flanks of the blacktail snowcrest uplift indicate that no thick cover of upper cretaceous or younger rocks extended over the flanks of the uplift during mississippian through permian time the area of later laram de uplift underwent more rapid subsidence than the area of the laramide ruby syncline and the centennial basin to the southeast the inferred sub snowcrest range thrust fault apparently represents a reactivated zone of basement weakness the intersection of thrust belt and foreland trends similar to the uinta uplift area to the south probably formed a number of structural traps for hydrocarbons which have not yet been tested potential petroleum source beds and reservoir rocks are both present in southwest montana however remnants of tertiary lava flows through much of the area tertiary to recent basin and range faulting and supermaturity with respect to oil of permian and older rocks in the western centennial uplift area are additional factors which must be considered in any estimate of hydrocarbon potential of the cordilleran overthrust belt and adjacent foreland in extreme southwestern montana

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

respiration dissolution and the lysocline 1 here i synthesize the results of several types of measurements of organic carbon respiration and calcium carbonate dissolution rates in pelagic seafloor sediments measurements of pore water oxygen demonstrate that most of the respiration takes place very near the sediment water interface with a scale depth of a few millimeters the remainder of the oxic respiration occurs much deeper in the sediments with a scale depth of several centimeters all measures of respiration from locations as disparate as the tropical pacific and atlantic and the subtropical north atlantic agree that pelagic seafloor rates of oxic respiration of organic carbon are relatively independent of depth and location with the exception of sediments beneath the pacific eastern equatorial upwelling zone calcite dissolution in seafloor sediments requires forcing by respiration produced co2 and rates are consistent with a first order dependence on pore water undersaturation solubility as determined by mucci 1983 at atmospheric pressure and locally variable mass specific dissolution rate constants respiration driven calcite dissolution fluxes predicted by this combination of respiration and dissolution rate expressions are significantly lower than many previous estimates comparison of dissolution fluxes in the oligotrophic open ocean measured by other researchers with benthic chamber incubation techniques with those predicted by this combination of rate expressions is within stated uncertainties in agreement in all but one case questioning the need for complicated mechanisms such as surface buffering or authigenic precipitation to explain seafloor calcite diagenesis applying these kinetics to a simple one dimensional steady state model of the bulk calcite content and sediment accumulation rates of the sediment mixed layer yields results consistent with observations of the seafloor lysocline the region of transition from high calcite to low calcite sediments on the ceara rise in the western tropical north atlantic and the ontong java plateau in the western equatorial pacific scenarios ignoring dissolution driven by respiration produced co2 in pore waters and using the high order dependence on undersaturation and very large dissolution rate constants implied by some earlier laboratory studies do not simulate these observations while the scheme represented here does in fact imply a strong shift in the locus of carbonate dissolution toward the sediment water interface as bottom water saturation decreases as implied by the observations of martin et al 2000 no simple combination of sediment transport coefficients and reaction kinetics can reproduce the observation of increasing 14c age as dissolution progresses these results emphasize the importance of accurate knowledge of the kinetics of respiration and dissolution to interpretation of either the present day or paleolysocline

the early messinian velona basin siena central italy paleoenvironmental and paleobiogeographical reconstructions abstract a multi disciplinary study of the basal lacustrine succession of the velona basin tuscany central italy provides informations about the paleoenvironmental and paleogeographical evolution of a post collisional basin located in the mediterranean area detailed sedimentological paleontological molluscs ostracods mammals charophytes and pollen and geochemical analyses on biogenic carbonates were carried out on a 66 m thick muddy sandy succession integrating the vertical distribution of selected species of ostracods and molluscs with the range of the mammal assemblage it has been possible to correlate the basal succession of the velona basin to the early messinian pre evaporitic corresponding to the lower part of the mn 13 zone the basal portion of the velona filling deposits corresponds to an unstable shallow lacustrine marshy environment rich in aquatic vegetation surrounded by swamps dominated by taxodiaceae and uplands dominated by warm temperate deciduous forests waters were generally brackish oligo mesohaline alternating with hypohaline episodes salinity changes recorded by the faunal assemblages do not parallel with changes in the geochemical signatures in ostracod shells and charophyte gyrogonites geochemistry of biogenic carbonates points to an athalassic origin of the water salinity probably linked to the dissolution of the triassic evaporites of the basement thus the absence of connections between the velona basin and the mediterranean sea during early messinian is confirmed ostracods molluscs and mammals show a central european paleobiogeographical affinity showing that at the time of deposition of the velona filling deposit the endemic tusco sardinian paleobioprovince was already disrupted and the northwards connections were noticeable on the other hand ostracods do not show any paleobiogeographic affinity with the ostracod assemblages of the paratethyan realm suggesting that no links between mediterranean and paratethys were present at that time

carbonate compensation dynamics 1 carbonate saturation zsat and compensation zcc depths change with deep ocean acidification and basification we present simple explicit mechanistic formulas for the positions of these two critical depths in particular zcc is expressed as a function of the mean dissolved carbonate ion concentration of the deep ocean co3 d the supply of dissolvable caco3 fc and the dissolution rate constant at the sediment water interface kc which we show to be essentially mass transfer controlled calculations reveal that zsat and zcc are today some 0 9 km apart and will rise and separate by as much as 1 7 km with acidification conversely if co3 d increases zsat and zcc will deepen but their separation will asymptote to 0 7 km

sr nd hf isotopes along the pacific antarctic ridge from 41 to 53 s 1 major trace element and sr nd hf isotope data in basalts collected along the pacific antarctic ridge par axis between 53 and 41 s far from any hotspot influence reveal tight coherent geochemical variations within the depleted morb mantle all samples are located below the pacific reference line defining two sub oceanic mantle domains on each side of the easter microplate the data extend the par 66 53 s field towards more radiogenic sr 0 70264 less radiogenic nd 7 7 and hf 11 4 values the along ridge geochemical variability is closely related to the morphological segmentation of the ridge anomalous geochemical features are attributed to the atypical morphology of two segments due to the presence of off axis magmatism the first order ridge discontinuity defined by the menard transform fault separates two slightly different mantle domains each with its own history

late quaternary sea level changes along the tyrrhenian coast near orbetello tuscany central italy palaeoenvironmental reconstruction using ostracods abstract a multidisciplinary study has been carried out on a 51 m long core drilled on coastal lowlands near the albegna river tuscany central italy both sedimentological and faunal analyses ostracods and molluscs indicate a coastal lagoon environment repeatedly influenced both by the rising holocene sea and the albegna river alluvial inflow 13c 18o mg ca sr ca and 87sr 86sr analyses were performed on cyprideis torosa shells in order to detail the influence of albegna river freshwater on the coastal lagoon water the analytical data illustrate the difficulties of using geochemical proxies in marginal marine settings four radiocarbon dates provide a chronostratigraphy for the early holocene part of the core the data are used to reconstruct late pleistocene to early holocene palaeoenvironments along this part of the coast and show the development of freshwater environments followed by a coastal brackish lagoon formed in response to the initial holocene rapid rise in relative sea level an attempt is made to relate sediments and age data from the core to the relative sea level curve for the tyrrhenian sea

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

the geometry of folded and thrusted rocks in the rocky mountain foothills near grande cache alberta lower cretaceous clastic rocks make up the inner foothills of the rocky mountains along the smoky river near grande cache alberta shortening of these rocks is accomplished by folding and thrusting and averages 33 over the area studied folds in the area are of the chevron variety they are caused by shortening of a multilayered sequence of alternating competent and incompetent strata where the thickness of the competent layers is fairly constant the folds are generally cylindrical and maintain their shapes over distances of up to 2 km along trend however at their tapering ends they are conical the majority of the faults are southwest dipping thrusts displaying ramps that cut up stratigraphic section and flats that are parallel to bedding the best exposed fault in the area is the mason thrust displacements along this fault increase from 150 m in the northwest to 1500 m in the southeastern part of the area a prominent anticline below the mason thrust diminishes gradually towards the southeast a conical fold with a half apical angle of 7 describes this geometry shortening by this fold decreases from about 30 in the northwest to 10 in the southeastern part of the area this indicates that a decrease in shortening by folding is compensated by an increase in thrust fault displacement it is an example of fault to fold displacement transfer

late miocene palaeoenvironmental evolution of the baccinello cinigiano basin tuscany central italy and new autoecological data on rare fossil fresh to brackish water ostracods abstract this paper reports the results of palaeoecological analyses on fossil ostracod communities of the tortonian and messinian deposits cropping out in the baccinello cinigiano basin a tuscan central italy post collisional continental basin through multivariate analyses such as cluster analysis upgma and detrended correspondence analysis dca several physico chemical variations in the water body have been recognised the more ancient middle late tortonian lacustrine environment was characterised by a shallow proximal and a deep distal facies with oligo mesohaline waters during this stage the salinity of the lake water was controlled by the dissolution of triassic evaporites buried at shallow depth in the basin instead the subsequent lower messinian fluvio lacustrine environment was characterised by shallow freshwater habitats with variable water flow conditions during the uppermost lower messinian the lake was deep and contained brackish water again these reconstructions add new information on the variability of several ecological parameters such as depth salinity and water flow conditions and help to clarify the autoecology of poorly known fossil ostracods within the fossil genus tavanicythere the species tavanicythere irregularis tavanicythere parva and tavanicythere sp q are adapted to deep and saline waters tavanicythere lepida is a shallow and less saline water inhabiting species while tavanicythere nodosa occupies an intermediate position with respect to palaeodepths and palaeosalinities within the genus loxoconchissa loxoconchissa loxoconchissa kinoi and loxoconchissa loxocaspia tuberosa are characteristic of an oligohaline and deep environment while loxoconchissa loxocaspia nuda and loxoconchissa loxocaspia sp 1 are more halophile species potamocypris gracilis is a polyrheophilic and rather profundal species that can tolerate shallower depths paralimnocythere bicornis is a freshwater to slightly halophylic and reophobic species vestalenula sp is one of the few known vestalenula species that can withstand slightly saline waters

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

relating estimates of caco3 production export and dissolution in the water column to measurements of caco3 rain into sediment traps and dissolution on the sea floor a revised global carbonate budget 1 the global caco3 budget is constrained by new estimates of standing stocks fluxes through the water column and dissolution in the water column and on the sea floor previous estimates of carbonate production and export are indistinguishable within a large range of values 0 4 1 8 gt pic yr 1 globally excess alkalinity ta and water mass tracers indicate dissolution of 1 0 gt pic yr 1 between 200 and 1500 m suggesting production and export must at least equal this amount most water column dissolution occurs at high latitudes and alkalinity fluxes from outer shelf and upper slope sediments 100 1500 m only support 5 10 of the ta inventory below 2000 m the sinking flux of pic 0 6 gt pic yr 1 is consistent with the rate of sea floor dissolution 0 4 gt pic yr 1 plus burial 0 1 gt pic yr 1 this rain rate constrains the export value to 1 6 gt pic yr 1 satellite based estimates of standing stocks of caco3 indicate a decrease equatorward which is opposite in trend to sediment trap fluxes this observation may be explained by an equatorward decrease in sinking particle dissolution systematic changes in pic residence time with latitude or satellite retrieval problems globally averaged euphotic zone standing stock 5 4 mmol m 2 and export estimates indicate pic residence times of 5 18 days

variation in fault behaviour in different tectonic provinces of new zealand abstract fault behaviour appears to be different in different tectonic provinces of new zealand uplifted holocene marine terraces along the east coast of the north island suggest time predictable behaviour on reverse faults of the hikurangi subduction margin major dextral faults of the strike slip fault province in central new zealand appear to show characteristic slip behaviour short normal faults in the central volcanic region show highly variable increments of displacement finally reverse faults of the central otago and northwest nelson region may have intermittently characteristic patterns of activity each of these behaviour patterns has been observed elsewhere although where there are good data to constrain the actual dates of palaeoearthquakes a uniform slip or coupled model best explains most situations temporal and spatial clustering of fault rupture and major earthquakes are increasingly being recognized it is crucial to obtain better dates and to determine the extent of individual rupture segments in order to better characterize fault behaviour non characteristic fault behaviour has serious implications for current methods of seismic hazard evaluation seismic hazard studies should utilize specific fault data in preference to assuming a particular fault behaviour model

laramide thrust generated alluvial fan sedimentation sphinx conglomerate southwestern montana the uppermost cretaceous lower tertiary sphinx conglomerate crops out over an area of approximately 20 km2 8 mi2 in the madison range of southwestern montana the sphinx consists of more than 1 000 m 3 300 ft of synorogenic boulder and cobble conglomerate derived from a late cretaceous laramide uplift that was located in the area presently occupied by the madison river valley palynological and radiometric age data indicate that the sphinx was deposited 75 58 ma and that thrusting and folding of the deposit had largely ceased by 56 ma compositions of sphinx clasts and paleocurrent data indicate that the sphinx was produced by uplift and unroofing of mesozoic and paleozoic rocks located on two thrust sheets to the west and southwest the lower s hinx was deposited on the distal portions of an eastward prograding alluvial fan system clast assemblages and lithofacies indicate that deposition of the middle sphinx was controlled by a combination of progradation in response to ongoing thrusting and an influx of resistant clasts derived from middle paleozoic carbonates in the source area deposition of the upper sphinx was probably controlled by source lithology as the influx of very coarse resistant clasts from middle and lower paleozoic carbonates overwhelmed the fan system s ability to organize its load of sediment by normal fan processes a preliminary facies model for thrust generated alluvial fan deposits predicts intraformational deformation cannibalization of proximal synorogenic fan facies and abrupt compositional breaks in response to episodes of thrusting

aragonite dissolution kinetics and calcite aragonite ratios in sinking and suspended particles in the north pacific the lack of consensus on caco 3 dissolution rates and calcite to aragonite production and export ratios in the ocean poses a significant barrier for the construction of global carbon budgets we present here a comparison of aragonite dissolution rates measured in the lab vs in situ along a transect between hawaii and alaska using a 13 c labeling technique our results show a general agreement of aragonite dissolution rates in the lab versus in the field and demonstrate that aragonite like calcite shows a non linear response of dissolution rate as a function of saturation state total carbon fluxes along the n pacific transect in august 2017 as determined using sediment traps account for 11 23 weight of total mass fluxes in the upper 200 m with a pic particulate inorganic carbon poc particulate organic carbon mole ratio of 0 2 0 6 a comparison of fluxes at depths of 100 m and 200 m indicates that 30 60 pic dissolves between these depths with 20 70 attenuation in poc fluxes the molar ratio of pic to poc loss is 0 29 the simultaneous loss of pic and poc in the upper 200 m potentially indicates pic dissolution driven by organic matter respiration or metazoan zooplankton consumption the calcite aragonite ratio in trap material is significantly lower in the subtropical gyre than in the subarctic gyre aragonite fluxes vary from 0 07 to 0 38 mmol m 2 day 1 at 100 m and 0 06 to 0 24 mmol m 2 day 1 at 200 m along the north pacific transect with no specific trend over latitude the identification of suspended pic mineral phases by raman spectroscopy shows the presence of aragonite below 3000 m in the subtropical gyre but none in the subpolar gyre these multiple lines of evidence suggest that predictions based on a strictly thermodynamic view of aragonite dissolution combined with measured aragonite fluxes underestimate observed alkalinity excess and measured pic attenuation in sinking particles our measured aragonite flux combined with our inorganic dissolution rate only account for 9 and 0 2 of the excess alkalinity observed in the north pacific feely et al 2004 assuming aragonite sinking rates of 1 m day 1 and 100 m day 1 respectively however respiration driven dissolution or metazoan zooplankton consumption indicated by the simultaneous attenuation of pic and poc in sediment traps is able to generate the magnitude of dissolution suggested by observed excess alkalinity

the effect of orthophosphate on carbonate mineral dissolution rates in seawater the dissolution kinetics of a variety of synthetic and biogenic carbonates low mg calcite mg calcite and aragonite were investigated in gulf stream seawater salinity s 35 spiked with orthophosphate to a concentration of 50 m phosphate is known to inhibit calcite dissolution and has been reported to catalyze the dissolution of aragonite the main goal of the study was to assess whether the degree of inhibition depends on the mineralogy of the dissolving carbonate phase dissolution experiments were conducted at 25 c and a pco2 of 10 2 5 atm using the ph stat technique dissolution rates were measured at saturation states ranging from 0 1 to 0 8 times saturation with respect to the dissolving carbonate mineral and were compared to rates measured in low phosphate seawater the degree of inhibition caused by phosphate addition increased as saturation state with respect to the dissolving carbonate mineral increased at a saturation state of 0 2 addition of phosphate reduced dissolution rates by about a factor of 2 closer to equilibrium at a saturation state of 0 8 dissolution rates were reduced by about a factor of 4 more importantly all carbonate samples whether of synthetic or biogenic origin were inhibited to similar degrees at equivalent saturation states the catalysis reported by previous workers for synthetic aragonite appears to be an artifact of its anomalous non linear dissolution rate over time because phosphate inhibits the dissolution of different carbonate minerals to similar degrees selective dissolution of aragonite from metastable carbonate sediments cannot be promoted by the presence of orthophosphate

calibration of the b ca proxy in the planktic foraminifer orbulina universa to paleocene seawater conditions the b ca ratio of planktic foraminiferal calcite a proxy for the surface ocean carbonate system displays large negative excursions during the paleocene eocene thermal maximum petm 55 9 ma consistent with rapid ocean acidification at that time however the b ca excursion measured at the petm exceeds a magnitude that modern ph calibrations can explain numerous other controls on the proxy have been suggested including foraminiferal growth rate and the total concentration of dissolved inorganic carbon dic here we present new calibrations for b ca versus the combined effects of ph and dic in the symbiont bearing planktic foraminifer orbulina universa grown in culture solutions with simulated paleocene seawater elemental composition high ca low mg and low total boron concentration b t we also investigate the isolated effects of low seawater b t high ca reduced symbiont photosynthetic activity and average shell growth rate on o universa b ca in order to further understand the proxy systematics and to determine other possible influences on the petm records we find that average shell growth rate does not appear to determine b ca in high calcite saturation experiments in addition our paleocene calibration shows higher sensitivity than the modern calibration at low b oh 4 dic given a large dic pulse at the petm this amplification of the b ca response can more fully explain the petm b ca excursion however further calibrations with other foraminifer species are needed to determine the range of foraminifer species specific proxy sensitivities under these conditions for quantitative reconstruction of large carbon cycle perturbations

dynamics of benthic marine communities across the early middle pleistocene boundary in the mediterranean region valle di manche southern italy biotic and stratigraphic implications abstract the valle di manche vdm section calabria southern italy offers the opportunity to investigate the ostracod turnover along a continuous shelf succession straddling the early middle pleistocene boundary and compare it against other paleoenvironmental i e mollusks and paleoclimatic uvigerina peregrina 18o records high resolution ca 1 sample m ostracod fauna quantitative data coupled with gradient analysis detrended correspondence analysis and non metric multi dimensional scaling document a strong relationship between changes in faunal composition and lithofacies vertical stacking patterns the comparison between the mollusk and ostracod derived ordination data demonstrates that the meio and macro faunal turnover is guided by a common complex gradient bathymetry the integrated ostracod mollusk gradient analysis also provides a trend in water depths along the section highlighting to what extent such multivariate approach can improve the paleoenvironmental and sequence stratigraphic interpretation of ancient shallow marine successions when plotted stratigraphically ordination major axis sample scores reveal two increasing decreasing patterns in water depth that fit well with the t r cycles previously identified paleobathymetric estimates combined with the vertical distribution of key ostracod groups i e epiphytic taxa on sandy substrates vs deep sea mud related taxa allow refining depositional trends stratal stacking patterns and position of previously not well resolved sequence stratigraphic surfaces within each t r cycle e g transgressive surface ts indeed two rapid increases in water depth values mark the tss that separate shallowing upward progradational rst from deepening upward retrogradational tst stratal stacking patterns of shelf deposits the tss which underline fine grained successions dominated by deep sea mud lover taxa are invariably constrained to the inception of interglacials marine isotope stages mis 21 and 19 identified within the vdm section by benthic foraminifera 18o values within both the vdm t r cycles the deepest conditions ca 140 m of water depth are invariably identified within the neopycnodonte unit slightly above the lightest 18o intervals the overlying decreasing bathymetric trend coupled with shifts in ostracod ecological groups allows to identify in the bryozoans lithofacies the stillstand falling of the relative sea level also tracked by a progressively heavier 18o record more stable paleobathymetric conditions around 40 45 m of water depth characterize the overlying silt sand deposits dominated by epiphytic species and showing the heaviest 18o values

relay zones between mesoscopic thrust faults in layered sedimentary sequences abstract we examine the geometry formation and destruction of relay zones in well bedded sedimentary sequences containing thrust fault segments with maximum observed displacements of 0 64 8 m contractional extensional and neutral relay zones are distinguished based on the stepping sense of the interacting fault segments and the orientation of the associated fault slip vectors large displacement gradients 0 17 1 0 in relay zones are mainly accommodated by folding with aggregate displacements maintained across segment boundaries and a significant component of the fault slip converted to fold related shortening folds in contractional relay zones verge in the direction of hanging wall motion with the steeper limb defining a parallelogram shaped zone between thrusts fault segment lengths are established after minimal displacement and folds in relay zones grow between segments as displacement accrues on the thrusts with increasing displacement upper and lower thrust tip lines in contractional and extensional relay zones are fixed at stratigraphic boundaries while the lateral thrust tip lines may propagate in a strike parallel direction upper and lower tip lines may eventually propagate to bypass relay zones that formed early in the fault growth history contractional relay zones remain intact at higher displacements than extensional relay zones

late messinian lago mare ostracod palaeoecology a correspondence analysis approach abstract in this paper two different italian late messinian lago mare ostracod assemblages dominated mainly by extinct paratethyan species have been analysed by means of detrended correspondence analysis dca the obtained plots have been compared and with the help of the limited autoecological data on similar living species and geochemical data on the sediments in which they were included the autoecology and synecology of the lago mare assemblages have been inferred in particular it seems reasonable to suppose that 1 assemblages made only by pointed candonids are typical of rather deep possibly less than one hundred meters of depth and freshwater oligohaline environments 2 assemblages mainly composed of leptocytheridae point to shallow probably few tens of meters of depth and mesohaline waters 3 diversified and even assemblages made both by pointed candonids and leptocytheridae are common in rather deep less than one hundred meters of depth but oligo low mesohaline environments 4 caspiocypris seems rather tolerant of brackish salinities but prefers shallow environments 5 tyrrhenocythere could be an indicator of shallow and fresh oligohaline waters 6 cyprideis is an indicator of shallow waters but can withstand a very wide salinity range

global calcite cycling constrained by sediment preservation controls 1 we assess the global balance of calcite export through the water column and burial in sediments as it varies regionally we first drive a comprehensive 1 d model for sediment calcite preservation with globally gridded field observations and satellite based syntheses we then reformulate this model into a simpler five parameter box model and combine it with algorithms for surface calcite export and water column dissolution for a single expression for the vertical calcite balance the resulting metamodel is optimized to fit the observed distributions of calcite burial flux we quantify the degree to which calcite export saturation state organic carbon respiration and lithogenic sedimentation modulate the burial of calcite we find that 46 of burial and 88 of dissolution occurs in sediments overlain by undersaturated bottom water with sediment calcite burial strongly modulated by surface export relative to organic carbon export we find surface calcite export skewed geographically toward relatively warm oligotrophic areas dominated by small prokaryotic phytoplankton we assess century scale projected impacts of warming and acidification on calcite export finding high sensitive to inferred saturation state controls with respect to long term glacial cycling our analysis supports the hypothesis that strong glacial abyssal stratification drives the lysocline toward much closer correspondence with the saturation horizon our analysis suggests that over the transition from interglacial to glacial ocean a resulting 0 029 pgc a 1decrease in deep atlantic indian and southern ocean calcite burial leads to slow increase in ocean alkalinity until pacific mid depth calcite burial increases to compensate

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

active ooid growth driven by sediment transport in a high energy shoal little ambergris cay turks and caicos islands ooids are a common component of carbonate successions of all ages and present significant potential as paleoenvironmental proxies if the mechanisms that control their formation and growth can be understood quantitatively there are a number of hypotheses about the controls on ooid growth each offering different ideas on where and how ooids accrete and what role if any sediment transport and abrasion might play these hypotheses have not been well tested in the field largely due to the inherent challenges of tracking individual grains over long timescales this study presents a detailed field test of ooid growth hypotheses on little ambergris cay in the turks and caicos islands british overseas territories this field site is characterized by westward net sediment transport from waves driven by persistent easterly trade winds this configuration makes it possible to track changes in ooid properties along their transport path as a proxy for changes in time ooid size shape and radiocarbon age were compared along this path to determine in which environments ooids are growing or abrading ooid surface textures petrographic fabrics stable isotope compositions 13 c 18 o and 34 s lipid geochemistry and genetic data were compared to characterize mechanisms of precipitation and degradation and to determine the relative contributions of abiotic e g abiotic precipitation physical abrasion and biologically influenced processes e g biologically mediated precipitation fabric destruction through microbial microboring and micritization to grain size and character a convergence of evidence shows that active ooid growth occurs along the transport path in a high energy shoal environment characterized by frequent suspended load transport median ooid size increases by more than 100 m and bulk radiocarbon ages decrease by 360 yr westward along the 20 km length of the shoal crest lipid and 16s rrna data highlight a spatial disconnect between the environments with the most extensive biofilm colonization and environments with active ooid growth stable isotope compositions are indistinguishable among samples and are consistent with abiotic precipitation of aragonite from seawater westward increases in ooid sphericity and the abundance of well polished ooids illustrate that ooids experience subequal amounts of growth and abrasion in favor of net growth as they are transported along the shoal crest overall these results demonstrate that in the ambergris system the mechanism of ooid growth is dominantly abiotic and the loci of ooid growth is determined by both carbonate saturation and sediment transport mode microbes play a largely destructive rather than constructive role in ooid size and fabric

structural development of an archean orogen western point lake northwest territories the point lake orogen in the central archean slave province of northwestern canada preserves more than 10 km of structural relief through an eroded antiformal thrust stack and deeper anastomosing midcrustal mylonites fault restoration along a 25 km long transect requires a minimum of 69 km slip and 53 km horizontal shortening in the western part of the orogen the basal decollement places mafic plutonic volcanic rocks over an ancient tonalitic gneiss complex ten kilometers to the east in the keskarrah bay area slices of gneiss unroofed on brittle thrusts shed molasse into several submerged basins conglomerates and associated thinly bedded sedimentary rocks are interpreted as channel levee and overbank facies of this thrust related sedimentary fan system the synorogenic erosion surface at the base of the conglomerate truncates premetamorphic or early metamorphic thrust faults formed during foreland propagation while other thrusts related to hinterland progressing imbrication displace this unconformity tightening of synorogenic depositional troughs resulted in the conglomerates present localization in synclines to the west of associated thrust faults and steepening of structural dips eastern parts of the orogen consist of isoclinally folded graywackes composed largely of mutti and ricci lucchi turbidite facies b c and d interpreted as submarine fan deposits eroded from a distant volcanic arc thrust faults in the metasedimentary terrane include highly disrupted slate horizons with meter scale duplex structures and recrystallized calcmylonites exhibiting sheath folds and boudin trains with very large interboudin distances the sequence of fabric development and the overall geometry of this metasedimentary terrane strongly resembles younger forearc accretionary prisms conditions of deformation along the thrusts parallel the regional metamorphic zonation amphibolite facies in the basal decollement through greenschist facies shear zones to cataclastic crush zones in the region of emergent thrusts in keskarrah bay depth differences can account for only half of the metamorphic gradient thermal profiles which increased downwards in obducted greenstone belts and synthrusting plutonism explains other high metamorphic gradients a tectonic model involving the collision of an accretionary prism with a continental margin best explains the structural and sedimentological evolution of the orogen

estimates of the resistance to chemical transport posed by the deep sea boundary layer1 2 a strategy has been developed to permit the in situ calibration of measurements made with benthic chambers of chemical fluxes across the sediment water interface the resistance to chemical transport posed by the boundary layer is estimated using chemical transport techniques in benthic flux chamber mock ups and on the sea floor dissolution from gypsum alabaster plates is measured both inside and outside the flux chambers cacoo dissolution and radioisotope uptake techniques are suitable for laboratory and deep sea calibration of benthic fluxes broadly concordant resistance estimates have been achieved within flux chambers with these three quite different approaches an estimate of 470 p for the equivalent stagnant boundary film thickness has been made by the alabaster method on the sea floor at manop site h in the eastern pacific the transport of mn2 from the bottom waters to site h nodules if controlled by diffusion through a film of this thickness would be sufficient to explain their growth rates