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

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

carbonate recrystallization in shallow marine environments a widespread diagenetic process forming micritized grains abstract integrated morphologic petrographic and mineralogic analyses of sediment grains of the miliolid foraminifer archaias and the green alga halimeda from shallow marine environments in florida the bahamas and belize document pervasive syndepositional recrystallization in these grains scanning electron microscopy shows that original skeletal rods and needles recrystallize on the sea floor to a variety of equant micritic fabrics in thin section this textural alteration corresponds to progressive micritization with loss of the familiar golden brown color exhibited by fresh miliolids and halimeda and gradual development of gray cryptocrystalline carbonate x ray diffraction and electron microprobe studies show that this textural alteration may be accompanied by mineralogical changes from mg calcite to aragonite or from aragonite to mg calcite our findings support petrographic studies that reported syndepositional recrystallization in a wide variety of carbonate grains about thirty years ago but which have been largely ignored together these studies indicate that carbonate recrystallization is a widespread process of early diagenesis extensive recrystallization in shallow tropical seas challenges basic principles regarding the setting and timing of textural and mineralogic alteration of metastable carbonate grains in addition recognition of recrystallization as an important process of micritization contradicts prevailing theories that micritization results solely by infilling of microborings finally our findings raise fundamental questions concerning the nature of carbonate crystal structure mechanisms of crystal growth and driving forces for recrystallization answering these questions will require sedimentologists to step beyond traditional bounds into fields such as biomineralization and materials science

organic matter oxidation and aragonite diagenesis in a coral reef abstract a combination of field and theoretical work is used to study controls on the saturation state of aragonite inside a coral reef framework a closed system ion speciation model is used to evaluate the effect of organic matter oxidation on the saturation state of aragonite the aragonite saturation state initially drops below 1 but becomes oversaturated during sulfate reduction the c n ratio of the organic matter affects the degree of oversaturation with n poor organic material resulting in a system more corrosive to aragonite precipitation of sulfide as fes strongly affects the aragonite saturation state and systems with much fes formation will have a stronger tendency to become oversaturated with respect to aragonite both precipitation and dissolution of aragonite are predicted at different stages of the organic reaction pathway if the model system is maintained at aragonite saturation field data from a coral reef framework indicate that the system maintains itself at aragonite saturation and model predicted changes in dissolved calcium follow those observed in the interstitial waters of the reef aragonite probably acts as a solid phase buffer in regulating the ph of interstitial waters because interstitial water in the reef has a short residence time the observed equilibration suggests rapid kinetics

early diagenesis of shallow water periplatform carbonate sediments leeward margin great bahama bank ocean drilling program leg 166 mineralogic petrographic and geochemical analyses of sediments recovered from two leg 166 ocean drilling program cores on the western slope of great bahama bank 308 m and 437 m water depth are used to characterize early marine diagenesis of these shallow water periplatform carbonates the most pronounced diagenetic products are well lithified intervals found almost exclusively in glacial lowstand deposits and interpreted to have formed at or near the seafloor i e hardgrounds hardground cements are composed of high mg calcite 14 mol mgco 3 and exhibit textures typically associated with seafloor cementation geochemically hardgrounds are characterized by increased 18 o and mg contents and decreased 13 c sr and na contents relative to their less lithified counterparts despite being deposited in shallow waters that are supersaturated with the common carbonate minerals it is clear that these sediments are also undergoing shallow subsurface diagenesis calculation of saturation states shows that pore waters become undersaturated with aragonite within the upper 10 m at both sites dissolution and likely recrystallization of metastable carbonates is manifested by increases in interstitial water sr and sr ca profiles with depth we infer that the reduction in mineral saturation states and subsequent dissolution are being driven by the oxidation of organic matter in this fe poor carbonate system precipitation of burial diagenetic phases is indicated by the down core appearance of dolomite and corresponding decrease in interstitial water mg and the presence of low mg calcite cements observed in scanning electron microscope photomicrographs

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

electron microprobe study of mg distribution in recent mg calcites and recrystallized equivalents from the pleistocene and tertiary abstract the effect of early freshwater diagenesis on mg distributions in former mg calcite cements was determined by electron microprobe analysis of two major groups of samples 1 mg calcites in recent limestones not yet exposed to freshwater and 2 tertiary recent mg calcites and recrystallized equivalents which have undergone freshwater exposure pristine mg calcites are characterized by a uniform mg concentration in contrast former mg calcites from the miocene of enewetak atoll most of which are now radiaxial prismatic calcites have a much greater variation in mg content and traverses across the calcites reveal definite trends mg content of the calcite is inversely correlated with abundance of inclusions some of the cloudy growth layers are due to infestation by endolithic organi ms fungi the small variation in mg content in original mg calcite cements is a valuable starting point to be aware of when interpreting mg trends in recrystallized equivalents mg content can be related to inclusion abundance in recrystallized former mg calcites but not in pristine mg calcites therefore mg trends in altered materials most likely reflect dissolution reprecipitation processes not original mg trends a likely cause for the low mg content associated with inclusion rich growth layers is relatively high rates of dissolution and reprecipitation in these relatively permeable layers in some cases the increased permeability is the result of infestation by endoliths such organisms may cause the cloudiness observed in some other radiaxial calcites

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

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

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

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

controls on carbonate mineral accumulation in bahamian basins and adjacent atlantic ocean sediments abstract carbonate mineralogical studies of surface bahamian periplatform ooze containing pelagic calcite as well as bank derived aragonite and magnesian calcite were coupled with studies of the carbonate chemistry of the waters overlying these sediments the presence of metastable aragonite and magnesian calcite in the periplatform ooze presents a unique opportunity to assess the relation between the extent of carbonate saturation in the water column and the disappearance of metastable carbonate minerals in an area of the north atlantic ocean where intermediate and deep waters are saturated with respect to calcite aragonite is present in the fine fraction of the surface sediment to a water depth of 4 800 m but decreases sharply below 4 000 m this is also the depth limit of the occurrence of pteropod tests and fragments in the coarse fraction of the sediment the aragonite compensation depth should be by extrapolation between 5 000 and 5 200 m the saturation depth with respect to aragonite was estimated to be located between 3 800 and 4 500 m this corresponds fairly well with the depth of a sharp decrease of the fine aragonite as well as the depth of pteropod disappearance magnesian calcite in the fine fraction of the sediment decreases irregularly with depth and disappears between 3 700 and 4 000 m the calculated saturation depth with respect to magnesian calcite 13 mole mgco3 is between 900 and 1 500 m at this depth a significant drop in the concentration of magnesian calcite occurs this decrease of magnesian calcite from 25 to 15 percent could be caused by both dissolution and the increasing distance of deeper waters from the banks however the higher values of specific alkalinity of the waters ranging between 750 and 2 000 m when compared with the alkalinity values of the sargasso sea at the same latitude are interpreted to be indicative that some dissolution of magnesian calcite occurs in the bahamian basins at these water dept s our results show depressed levels by 500 m or more of the aragonite saturation depth in the water column as well as of the depth of aragonite disappearance in the surface sediment when compared with open ocean studies in the northwest atlantic in addition our results indicate that fine magnesian calcite 12 to 13 mole mgco3 disappears 1 200 to 1 500 m above the extrapolated disappearance depth of aragonite this observation is consistent with results for experimental studies showing that aragonite is more stable in seawater than a magnesian calcite of 12 to 13 mole mgco3

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

enhanced ventilation of the north atlantic subtropical gyre thermocline during the last glaciation the ocean s intermediate1 6 and deep7 8 circulation are both known to have differed during the last glaciation from those of today but little is known about the history of the subtropical gyres variations in gyre processes should be closely linked to variations in global climate as gyre circulation is driven by air sea interactions and reflects the climate at the ocean surface the gyres are also a significant reservoir of carbon and nutrients so that gyre processes affect the distribution of carbon and nutrients in the oceans and thus atmospheric co2 here we use measurements of 13c and 18o in foraminifera from the bahamas to produce a detailed reconstruction of nutrient and temperature profiles in the thermocline during the last glaciation the thermocline of the glacial north atlantic subtropical gyre lacked the oxygen minimum that is characteristic of the modern ocean and was depleted in nutrients indicating greater more uniform thermocline ventilation at that time thus not only intermediate waters1 5 but the entire upper water column within the glacial north atlantic was depleted of nutrients moreover glacial thermocline waters were cooler had a steeper temperature gradient and a shallower base both the ventilation and the thermal structure of the glacial thermocline are consistent with what is known of the glacial climate9 14

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

diagenetic processes in holocene carbonate sediments florida bay mudbanks and islands the sedimentology mineralogy and pore fluid chemistry of seven cores from the holocene sediments of florida bay were studied to determine the physical processes and diagenetic reactions affecting the sediments the cores were taken in a transect from a shallow mudbank onto a small adjacent island jimmy key steady state models of pore fluid chemistry are used to estimate the rates of various reactions in the mudbank sediments little carbonate mineral diagenesis is taking place no change in sediment mineralogy is detectable and pore water profiles of ca2 mg2 and sr2 show only minor variation chloride concentrations indicate substantial biological mixing of seawater from the bay into the sediments in one of the cores pore water analyses of sulphate and alkalinity show only a low degree of sulphate depletion and a decreasing extent of sulphate reduction downcore models of sulphate reduction in the mudbank show that there is substantial chemical exchange between the sediment pore fluids and water from the bay probably as a result of bio irrigation the sulphate and alkalinity data also suggest that the underlying pleistocene rocks contain water of near normal seawater composition stratigraphic analysis and 13c analyses of the organic carbon in the sediments of the island cores show that the sediments were primarily deposited in a subtidal mudbank setting only the upper 20 30 cm is supratidal in origin nevertheless island formation had a significant effect on pore fluid chemistry and the types of diagenetic reactions throughout the sediment column chloride in the sediment pore fluids is more than twice the normal seawater concentrations over most of the depth of the cores the constant elevated chloride concentrations indicate that hypersaline fluids which formed in ponds on the island are advected downward through the sediments models of the chloride profiles yield an estimate of 2 5 cm yr 1 as a minimum advective velocity changes in pore water chemistry with depth are interpreted as indicating the following sequence of reactions 1 minor high mg calcite dissolution and low mg calcite precipitation from 0 to 35 cm 2 ca or mg sulphate dissolution and low mg calcite precipitation from 5 to 35 cm 3 dolomite or magnesite precipitation together with sulphate reduction from 35 to 55 cm and 4 little reaction below 55 cm in addition one or more as yet unidentified reactions must be taking place from 5 to 55 cm depth as an imbalance in possible sources and sinks of alkalinity is observed the imbalance could be explained if chloride is not completely conservative despite the pore fluid chemical evidence for diagenetic reactions involving carbonate minerals no changes in sediment mineralogy were detected in x ray diffraction analyses probably because of the comparatively young age of the island

shallow subsurface diagenesis of pleistocene periplatform ooze northern bahamas previous studies on early submarine diagenesis of periplatform carbonates have implied that these originally polymineralic aragonite magnesian calcite calcite sediments are susceptible to early diagenesis only in current swept open seaways or where surficially exposed by erosion on the seafloor it has also been proposed that while in the shallow subsurface periplatform oozes retain their original mineralogy for at least 200 000 400 000 yr and remain unlithified for tens of millions of years evidence is reported here for extensive calcitization and selective lithification of periplatform oozes of late pleistocene age in two piston cores collected from water depths of 1 000 m north of little bahama bank it is shown that shallow 30 m subsurface diagenesis can significantly alter the original mineralogy of periplatform oozes to predominantly calcite in less than 440 000 yr and that cementation by calcite can produce chalk ooze sequences within the same time frame periplatform oozes that originally contain a high percentage of bank derived magnesian calcite appear to have a higher diagenetic potential than those originally low in magnesian calcite shallow subsurface calcitization and fithification greatly reduce the diagenetic potential of periplatform carbonates and chalk ooze sequences apparently can persist for tens of millions of years and to burial depths of at least 300 m shallow subsurface diagenesis at water depths 1 000 m proceeds via dissolution of magnesian calcite and aragonite and reprecipitation of calcite as allochem fillings exterior overgrowths and cement it is speculated that density driven kohout convection where seawaters under saturated with respect to magnesian calcite and aragonite and saturated supersaturated with respect to calcite flow through the margins of carbonate platforms is the primary driving mechanism for shallow subsurface diagenesis removal of mg during early stages of deep seafloor and shallow subsurface diagenesis should increase the mg content of interstitial waters which is likely to increase the dolomitizing potential of kohout convection fluid flow

carbonate crusts around volcanic islands composition origin and their significance in slope stability abstract extensive carbonate crusts discovered forming on the slopes of seamounts in many parts of the world s oceans are providing extra stability to the volcanic edifices these crusts are hardgrounds composed of mixtures of volcaniclastic debris and bioclastic material in most cases cemented by calcite in the form of isopachous coatings around grains and pore filling spar such crusts which have been collected by a remotely operated vehicle rov are described here from moderate depth to deeper water slopes 180 820 m around the volcanic island of montserrat in the caribbean and from the nearby kick em jenny submarine volcano off grenada radiogenic 87sr 86sr isotope ratios from the carbonates give an indication of age up to 0 4 ma years old but they also demonstrate that some samples have been altered by hydrothermal volcanic processes to give ages much older than expected 14 to 18 ma based on the foraminifera present such alteration is also supported by carbon and oxygen isotope 13c and 18o ratios although most samples retain typical marine values in many cases 18o is usually a little more positive than expected from modern caribbean shallow water carbonates likely reflecting cooler water at their moderate depths of lithification just one sample from kick em jenny has very negative 13c 42 indicating methanogenesis crusts are also reported here from the mediterranean sea with an example described from kolumbo submarine volcano northeast of the santorini volcanic complex in the hellenic subduction zone that are similar in many respects to those from the caribbean typically the biota of the crusts consists of calcareous red algae commonly encrusting volcanic clasts foraminifera benthic some also encrusting and planktic subordinate serpulids bivalves pteropods and heteropods and rare deeper water corals some bioclasts are derived from shallower water others from the moderate depths of the slope itself and planktic fallout in addition there is evidence for the former presence of microbes from the occurrence of calcified filaments and peloids in intragranular cavities several generations of sponge borings are usually present as well as calcite cement dissolution and calcite replacement of aragonitic bioclasts and cement and sponge spicules originally opaline silica have taken place the carbonate crusts are attributed to seawater circulating within the surficial sediment in some cases mixing with hydrothermal fluid driven by geothermal and volcanic processes submarine volcanic slopes clearly provide a location for moderate depth carbonate production and cementation but a further significance of these hardgrounds is in stabilising seamounts enabling their slopes to avoid frequent collapse dissection and readjustment however when failure does occur larger scale submarine landslides involving coherent slabs are more likely

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

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

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

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

highstand versus lowstand deposition on carbonate platform margins insight from quaternary foreslopes in the bahamas abstract examples of both highstand and lowstand deposition have been identified on the upper platform slopes of the tongue of the ocean bahamas highstand deposits consist of a thick wedge of fine grained skeletal and non skeletal sands and carbonate muds derived predominantly from the platform and deposited on slopes of 25 28 these sediments were deposited subsequent to platform flooding and may be more than 30 m thick along open leeward margins in contrast lowstand deposits consists of coarse skeletal sands gravels and boulders deposited on primary depositional slopes of 35 45 these sediments were derived from fringing reefs along the marginal escarpment and deposited during the initial rise of sea level following the last lowstand these variations in depositional character result in a distinctive signature of highstand versus lowstand deposition for steep sided platforms and further elucidate the response of carbonate platforms to high magnitude 5th order scale 20 000 yrs fluctuations in sea level

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

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

in situ measurements of calcium carbonate dissolution rates in deep sea sediments benthic fluxes of alkalinity carbon dioxide and oxygen have been measured using an in situ incubation chamber at three sites manop sites c and s and pacflux site sc in the central equatorial north pacific at two carbonate rich sites c and sc a budget for oxygen alkalinity and tco2 fluxes indicate a net caco3 dissolution rate of approximately 0 4 mmol m 2 day 1 this rate is only 20 of previous estimates but is consistent with a dissolution rate constant predicted from laboratory experiments with deep sea sediments and derived from in situ flux measurements in sediments of the southern california borderland organic matter oxidation in the sediment column provides the acid for 60 100 of the calcium carbonate dissolution occurring at these sites with the remainder derived from undersaturated bottom water at a low carbonate site s no carbonate dissolution in the sediment or on the sea floor is apparent although sediment traps indicate a rain of caco3 through 3400 m the rates of remineralization relative to resuspension or erosion at this site must differ for organic carbon and calcium carbonate so that carbonate grains reaching the sea floor are physically removed by erosion or resuspension before they dissolve while organic carbon is largely oxidized before it can be physically removed

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

controls and development of late quaternary periplatform carbonate stratigraphy in walton basin northeastern nicaragua rise caribbean sea the late quaternary sedimentary record in periplatform oozes and muds deposited on the northern nicaragua rise results from the interplay of four main controls 1 input of pelagic carbonates and bank derived fine aragonite and magnesian calcite 2 input of siliciclastic sediments 3 dispersal and removal of sediments by the caribbean current and 4 partial seafloor dissolution of metastable carbonates high accumulation rates of the calcite coarse sediment fraction throughout the study area demonstrate that planktonic foraminiferal productivity peaked during interglacial stages neritic carbonate productivity also peaked during interglacial stages when bank and shelf tops along the nicaragua rise were submerged within the photic zone because the bank and shelf tops remained mostly exposed during glacial stages the surface area available for the neritic carbonate productivity was drastically reduced to a narrow band along the margins of pedro bank and the southern shelf of jamaica a large volume of siliciclastic sediments transported from the coastal area of south america and the eastern and western regions of jamaica were deposited during glacial stages within the eastern and western deep extensions of walton basin this finding contrasts with the input pattern of siliciclastic sediments in walton basin itself where the largest input of siliciclastic sediments occurred at each of the interglacial climatic optima corresponding to intervals of maximum sea level transgression finally cores in water depths exceeding 1100 m display during interglacial stages aragonite accumulation rates systematically lower than rates in cores from water depths shallower than 1100 m this indicates that some bank derived aragonite and magnesian calcite has been partially removed by seafloor dissolution in areas from water depths exceeding 1100 m results from this study on the northeastern nicaragua rise indicate that not only do offbank transport and water column saturation state influence the late quaternary record but also that the variable strength of the caribbean current and the proximity of sources for siliciclastic sediments have played a major role in the development of the late quaternary periplatform high resolution stratigraphy

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

sedimentary patterns and geometries of the bahamian outer carbonate ramp miocene lower pliocene great bahama bank core logging and high resolution seismic data from odp leg 166 were used to analyse deposits of the neogene miocene lower pliocene bahamian outer carbonate ramp ramp sediments are cyclic alternations of light and dark grey wackestones packstones with interbedded calciturbidite packages and minor slumps cyclicity was driven by high frequency sea level changes light grey layers containing shallow water bioclasts were formed when the ramp exported material whereas the dark grey layers are dominantly pelagic calciturbidites are arranged into mounded lobes with feeder channels internal bedding of the lobes shows a north directed shingling as a result of the asymmetrical growth of these bodies calciturbidite packages occur below and above sequence boundaries indicating that turbidite shedding occurred during third order sea level highstands and lowstands highstand turbidites contain shallow water components such as green algal debris and epiphytic foraminifera whereas lowstand turbidites are dominated by abraded bioclastic detritus gravity flow depocentres shifted from an outer ramp position during the early miocene to a basin floor setting during the late miocene to early pliocene this change was triggered by an intensification of the strength of bottom currents during the tortonian which was also responsible for shaping the convex morphology of the outer ramp the miocene and lower pliocene of the leeward flank of great bahama bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps the contrast between its sedimentary patterns and the well known upper pliocene quaternary slope facies associations of the flat topped great bahama bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base of slope successions

shallow burial diagenesis of deep water carbonates northern bahamas results from deep ocean drilling transects rates of burial diagenesis and subsurface distribution of chalk and limestone in modern deep water carbonate slopes were little known prior to 1985 when the ocean drilling program established two drill transects in the northern bahamas north of little bahama bank and in southwestern exuma sound from these transects different shallow burial along the accretionary north margin of little bahama bank the amount of lithified strata decreases seaward because of a decreasing volume of bank derived aragonite the rate of bulk carbonate calcitization increases seaward as the rate of diagenesis begins to match then exceed the rate of burial mineral controlled diagenesis is of little consequence below about 20 m subsurface only 30 km seaward of the bank margin along the bypass margin in exuma sound the extent of lithification increases downslope toward preferential accumulation of bank derived aragonite much higher accumulation rates and high percentages of aragonite along this margin sustain a still present mineral controlled diagenetic potential in limestone at 300 m from analogy of modern bahama slopes considerable diagenetic heterogeneity within the shallow burial realm may be expected along some ancient carbonate margins our results serve to illustrate carbonate mineral stabilization and early limestone formation with secondary porosity in a sea water mediated environment and they further highlight the high diagenetic potential of periplatform carbonates

a survey of volcanic deformation on java using alos palsar interferometric time series of the hundreds of volcanic centers throughout the indonesian archipelago few are adequately monitored for pre eruptive activity due to socioeconomic and logistical barriers with the result that volcanic hazards in the region are not well quantified the advent of satellite borne l band synthetic aperture radar provides an opportunity for detection and measurement of volcanic deformation over broad regions in heavily vegetated tropical island arcs we use data from the palsar instrument on the japanese alos satellite to conduct a comprehensive survey of volcanic deformation on the indonesian island of java over a time period of two years 2007 2008 to obtain the most complete temporally continuous record of ground deformation we use a temporally overlapping set of short time interval radar image pairs to produce a deformation time series consistent with previous results from other regions our survey suggests that volcanoes experiencing small eruptions are typically fed by magma bodies too small and or too shallow or deep to produce a recognizable insar signal however we identified a deformation event at lamongan volcano which is likely linked to a magmatic intrusion at several kilometers depth and a second one at slamet volcano at a shallower depth that may have been related to a subsequent eruption this initial test of a broad application of l band data allowed us to better define the satellite imaging criteria required for successful observation as well as developing a useful methodology for monitoring deformation over a wide region

coupling between sulfur recycling and syndepositional carbonate dissolution evidence from oxygen and sulfur isotope composition of pore water sulfate south florida platform u s a sulfur cycling in fe poor organic rich shelf carbonates known to have rapid rates of so4 2 reduction remains poorly studied despite the volumetric significance of shelf deposits in modern and ancient carbon budgets we investigated sulfur cycling in modern carbonates of the florida platform from end member depositional environments muddy sands from the atlantic reef tract and finer grained mudbank and island flank deposits from florida bay relations between pore water chemistry so4 2 co2 ca 2 cl and oxygen and sulfur stable isotope compositions of so4 2 require direct coupling between sulfur redox cycling and syndepositional carbonate dissolution oxygen isotope compositions of pore water sulfate were remarkably shifted away from the established value for marine so4 2 9 5 despite near normal so4 2 cl ratios chemical evolution was least in reef tract pore waters and greatest in florida bay relative to overlying seawater mudbank sediments exhibited sulfate depletion with 18oso4 and 34sso4 values both increasing by about 7 more bioturbated island flank sediments colonized by thalassia grass had a 5 increase in 18oso4 variable 34sso4 values 17 7 to 23 3 and exceptionally high ca 2 cl ratios the large excess of ca 2 up to 1 7 mm requires a much larger acid source than the amounts derived from utilization of dissolved o2 0 3 mm and small degrees of net so4 2 reduction 0 5 mm reduced a conceptual model was constructed using chemical and isotopic data on natural pore waters and on sulfate isotope fractionation factors obtained from sediment incubation experiments the model outputs show that pore water compositions can be explained by a redox cycle where microbial so4 2 reduction is followed by very efficient h2s oxidation thus maintaining virtually invariant so4 2 cl ratios the enhanced o2 transport may be driven by associated marine grass rhizome systems and microbial communities established in bioturbated sediments the net result of the cycle is that the rate of sulfide oxidation which is largely balanced by the rate of microbial sulfate reduction is stoichiometrically related to the rate of carbonate dissolution this is consistent with previously reported rates of carbonate dissolution 400 mol cm2 yr and average rates of sulfate reduction 200 mol cm2 yr from the florida platform and a 2 1 stoichiometry

microspar development during early marine burial diagenesis a comparison of pliocene carbonates from the bahamas with silurian limestones from gotland sweden comparison of ultrastructures in pliocene periplatform carbonates from the bahamas with silurian limestones from gotland sweden reveals that despite the differences in primary sediment composition and age they reflect a similar mechanism of lithification in both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis neither significant compression nor meteoric influence are necessary for the formation of calcite microspar a model is proposed for the process of microsparitic cementation of fine grained aragonite needle muds comprising four stages 1 unconsolidated aragonite dominated carbonate mud 2 precipitation of microspar that engulfs aragonite needles 3 dissolution of aragonite resulting in pitted surfaces of the microspar crystals and 4 slight recrystallization our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite

accumulation of bank top sediment on the western slope of great bahama bank rapid progradation of a carbonate megabank high resolution seismic profiles and submersible observations along the leeward slope of western great bahama bank show large scale export of bank top sediment and rapid progradation of the slope during the holocene a wedge shaped sequence up to 90 m thick is present along most of the slope and consists of predominantly aragonite mud derived from the bank since flooding of the platform 6 8 ka total sediment volume of the slope sequence is 40 80 that of holocene sediment currently retained on the bank maximum rates of vertical accumulation and lateral progradation are 11 15 m ka and 80 110 m ka respectively 10 to 100 times greater than previously known for periplatform muds slope deposition of exported mud during sea level highs appears to have been a major mechanism for the westward progradation of great bahama bank throughout the quaternary this may provide a critical modern analogue for ancient progradational margins

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

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

seismic expression of quarternary climatic cycles in the peri platform carbonate ooze of the northern bahamas stratigraphic physical and acoustic properties of peri platform carbonate sediments in an 18 m long piston core core 2218 655 m from northwest providence channel bahamas have been investigated the sediments range in age from recent to about 1 m y old there is a close correlation between changes of compressional wave velocity and quaternary climate as indicated by 18 o velocity correlates negatively to aragonite content water content and porosity whereas it correlates positively to grain size saturated bulk density and observed degree of cementation changes in the degree of cementation exert a particularly strong influence on velocity variations all parameters correlate to quaternary climate sea level fluctuations during glacial low sea level stages the aragonite content water content water content and porosity decrease but grain size saturated bulk density and the degree of cementation increase all of these increase velocity in general water content porosity and the aragonite content decrease slightly with core depth but grain size saturated bulk density degree of cementation and velocity increase slightly two processes may contribute to these trends 1 shallow subsurface diagenesis upon burial and 2 variations of both the interglacial production of bank top sediments and the intensity of glacial sea floor diagenesis major changes in velocity are associated with transitions from glacial to interglacial stages acoustic reflectors correlate one to one with the velocity changes occurring at isotopic stage boundaries 7 8 9 10 and 11 12 at the site of core 2218 deeper reflectors have an interference origin because velocity changes are more closely spaced the reflectors that correlate with isotopic stage boundaries can be used to study the detailed history of quaternary peri platform carbonate deposition and place it into the context of global climate sea level cycles

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

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

fluid flow through carbonate platforms constraints from 234u 238u and cl in bahamas pore waters the geometry timing and rate of fluid flow through carbonate margins and platforms is not well constrained in this study we use u concentrations and isotope ratios measured on small volumes of pore water from bahamas slope sediment coupled with existing chlorinity data to place constraints on the fluid flow in this region and by implication other carbonate platforms these data also allow an assessment of the behaviour of u isotopes in an unusually well constrained water rock system we report pore water u concentrations which are controlled by dissolution of high u organic material at shallow depths in the sediment and by reduction of u to its insoluble 4c state at greater depths the dominant process influencing pore water 234 u 238 u is alpha recoil in holocene sediments the increase of pore water 234 u 238 u due to recoil provides an estimate of the horizontal flow rate of 11 cm year but with considerable uncertainty at depths in the sediment where conditions are reducing features in the u concentration and 234 u 238 u profiles are offset from one another which constrains the effective diffusivity for u in these sediments to be1 2 10 8 cm 2 s 1 at depths between the holocene and these reducing sediments pore water 234 u 238 u values are unusually low due to a recent increase in the dissolution rate of grain surfaces this suggests a strengthening of fluid flow probably due to the flooding of the banks at the last deglaciation and the re initiation of thermally driven venting of fluid on the bank top and accompanying recharge on the slopes interpretation of existing chlorinity data in the light of this change in flow rate constrain the recent horizontal flow rate to be 10 6 3 4 cm year estimates of flow rate from 234 u 238 u and cl are therefore in agreement and suggest flow rates close to those predicted by thermally driven models of fluid flow this agreement supports the idea that flow within the bahamas banks is mostly thermally driven and suggests that flow rates on the order of 10 cm year are typical for carbonate platforms where such flow occurs 1999 elsevier science b v all rights reserved

isotopic signature of burial diagenesis and primary lithological contrasts in periplatform carbonates miocene great bahama bank the stable isotope geochemistry of miocene sediments from the leeward margin of the great bahama bank was examined to investigate burial diagenetic processes in periplatform carbonates data indicate that in addition to differences in bulk proportions of neritic and pelagic carbonate along the slope rhythmic variation in primary carbonate content has controlled patterns of burial diagenesis and associated geochemical signatures throughout much of the succession examined the present study focuses on ocean drilling program sites 1006 and 1007 the most distal of five sites drilled from marginal to deep basin environments during leg 166 these miocene sections are characterized by their cyclic appearance manifest as decimeter to meter scale alternations between light colored ooze chalk limestone and dark colored marl marlstone the section at site 1006 contains a high proportion of pelagic carbonate and is unlithified to a subbottom depth of 675 m fluctuations in 18 o and 13 c values at this site are independent of lithological variation and reflect primary conditions at site 1007 located at the toe of slope and composed of a mixture of bank derived and pelagic carbonate limestones are densely cemented show little evidence of compaction and have 18 o values up to 2 higher than coeval sediments at site 1006 marlstones at site 1007 are poorly cemented exhibit an increase in compaction related features with depth and have lower and more variable 18 o values that are similar to those of coeval sediments at site 1006 isotopic and petrographic characteristics of limestone interbeds result from cement precipitation from cold sea water during the first 100 m of burial higher proportions of insoluble materials and pelagic carbonate seem to have inhibited diagenetic alteration in adjacent marlstones in spite of significant compaction and pressure solution during burial original isoto pic compositions appear to be best preserved in these intervals at site 1007 the documented contrasts in petrographic and isotopic patterns illustrate the role of primary sediment composition in controlling lithification processes in periplatform carbonates and stress the importance of consid ering such factors when interpreting geochemical data from ancient shelf and slope limestones

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

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

crystal habit geochemistry and cathodoluminescence of magnesian calcite marine cements from the lower slope of little bahama bank the petrography and geochemistry of marine magnesian calcite cements recovered from the sea floor on the lower thermocline lower slope of little bahama bank address three issues concerning inorganic carbonates 1 crystal habit of marine magnesian calcite cements 2 cation composition of marine precipitates and 3 origins of cathodoluminescence in calcite bladed and blocky limpid spar cements formed contemporaneously within the same intraparticle pore as shown by banded cathodoluminescence traced without interruption through both cement habits bladed and blocky cements exhibit a positively covariant linear relationship for mg and sr having low proximal early formed compositions and high distal late formed compositions linear covariance of mg and sr is interpreted to indicate that the concentrations of these cations were controlled by kinetic effects as they formed with early precipitation occurring more rapidly than later precipitation precipitation rates apparently did not affect cement habit limpid isopachous bladed spar cements the distal third of which are brightly cathodoluminescent have a wide range of mg and sr compositions which is almost completely spanned by both distal cathodoluminescent and proximal noncathodoluminescent parts of cements occurring within the same pore mg and sr do not have a linear relationship these cements are interpreted to have recrystallized in deep cool sea water during recrystallization magnesium was lost and in some cases manganese the principal cathodoluminescence excitor was presumably gained

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

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

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

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

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

rapid burial diagenesis of deep water carbonates exuma sound bahamas well lithified deep water periplatform limestones of late miocene age occur at subsurface depths from 113 m to total depth of 283 m at ocean drilling program odp site 632 in exuma sound bahamas this occurrence marked by a dramatic increase in compressional wave velocities up to 5 0 km s represents the most rapid transformation of ooze to limestone yet discovered in either periplatform or open ocean settings the burial diagenetic pathway is similar to those for meteoric and deep burial diagenetic environments aragonite dissolves magnesian calcites exsolve or dissolve low mg calcite precipitates as cement and secondary moldic vuggy porosity develops stable isotope ratios suggest precipitation of low mg calcite from cold marine derived pore waters accelerated diagenesis is a response to the influx of large quantities up to 80 of bank derived metastable carbonates and rapid burial via high accumulation rates up to 210 m m y our findings 1 document carbonate mineral stabilization and lithification in a seawater mediated shallow burial diagenetic environment 2 highlight the very high diagenetic potential of periplatform carbonates and 3 call into question the use of seismic velocities as support for the bahama megabank hypothesis

whitings a sedimentologic dilemma whitings drifting clouds of water milky because of suspended carbonate have been claimed to originate from either the action of bottom feeding fish or direct precipitation of calcium carbonate five cruises during different seasons were made to the great bahama bank to collect data pertinent to the controversy measurements of particulate concentrations average 10 mg liter with a maximum of 20 mg liter of carbonate sediment suspended in whiting water compared with an average of 1 5 mg liter for clear water outside the whitings the particles are dominantly acicular aragonite but mg calcite composes as much as 20 percent of some whitings sedimentation rates measured with fixed and drifting sediment traps were as great as 34 g m 2 hr sediment suspended in whitings aggregated into silt and sand size fioccules and settled to the bottom of settling tanks within six hours even on a rocking ship sediment in artificial whitings created by stirring sediment from the bottom with a shrimp trawl settled to the bottom in about the same time natural whitings on the other hand were never observed to dissipate because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours we conclude that the natural whitings are continually replenished by direct precipitation the search for fish in whitings utilized sidescan sonar and fathometer imaging shrimp trawls rotenone remote video and direct scuba observation these methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most bahamian whitings several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend the distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish stable carbon and oxygen isotopic analyses and delta 14 c activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension estimates indicate that the amount of new carbonate produced in whitings on the great bahama bank is substantially higher than that arising from algal production consequently the amount of sediment transported to deep water may be much greater than previously thought

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

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