the origin of the millimeter scale lamination in the neoproterozoic lower beck spring dolomite implications for widespread fine scale layer parallel diagenesis in precambrian carbonates abstract the neoproterozoic lower beck spring dolomite exhibits a prominent millimeter scale light dark planar lamination commonly interpreted as a primary depositional fabric microscopic examination reveals that the dark laminae are composed of micrite and contain a micrometer scale wavy fabric whereas the light laminae are composed of relatively coarse crystalline pseudospar that engulfs surrounds and crosscuts the dark laminae nearly all of the light laminae surround or occur in proximity to elongate long axis fabric parallel spar filled cavity structures the average 18o values for dark and light laminae are 1 8 std dev 1 6 and 3 0 std dev 1 3 vpdb respectively cavity filling cements are even more depleted in 18o with an average isotopic value of 6 2 std dev 1 1 these characteristics suggest that the coarse crystalline light laminae are the result of the preferential aggrading neomorphism of a thinly laminated micritic host rock and that the now cemented cavity structures acted as conduits for the fluid responsible for recrystallization the oxygen isotope distributions are consistent with progressive recrystallization by an 18o depleted fluid likely of meteoric origin therefore we interpret the prominent millimeter scale light dark layering in the lower beck spring dolomite to result from widespread laminae parallel diagenetic processes perhaps controlled by fine scale layer parallel differences in initial porosity and permeability and not from primary sedimentary processes extensive layer parallel diagenesis on such a fine scale is rare in phanerozoic shallow marine deposits due to disruption by bioturbation however before the advent of metazoan burrowing fine scale layer parallel fluid flow would have been more common thus the diagenetic fabric of the lower beck spring dolomite may represent a mode of carbonate diagenesis restricted to the precambrian similar diagenesis may also occur in phanerozoic environments devoid of vertical bioturbation

the belize margin revisited 1 holocene marine facies belize is best known for its 260 km long barrier reef and associated lagoon reef shoals but also exhibits a complete transition from near shore siliciclastics to pure carbonate deposits across a narrow shelf lagoon and in addition has three of the very few occurrences of caribbean atolls published holocene facies relationships on the belize shelf have been semi quantitative in that they are based on quantitative point count thin section data in the northern shelf lagoon and on qualitative estimates of thin section composition in the southern shelf lagoon this contrast has been rectified by point counting southern shelf lagoon thin sections and incorporating the result with published point count data from the northern shelf supplemented by additional information to produce a modified factor analysis facies distribution for the entire shelf the resulting nine facies are extended seaward to include previously published analysis of sediment on the three belize off shelf atolls resulting in a total of 11 facies in addition the carbonate mud distribution has been mapped over both the shelf and atolls with the not unexpected result that in places the distribution pattern clearly indicates a barrier platform source of lagoon deposited carbonate mud dunham s limestone classification terminology has been used as a basis for description to make these relationships more useful to those reconstructing ancient limestone depositional environments

early dolomitization and recrystallization of carbonate in an evaporite basin the middle devonian ratner laminite in southern saskatchewan canada this study provides an example of early dolomitization of basinal limestone associated with a giant evaporite deposit the middle devonian ratner carbonate is extensively to completely replaced by microcrystalline to finely crystalline dolomite in the southern and central part of southern saskatchewan in the elk point basin in the northern part however individual cored intervals of the ratner laminite are either completely dolomitized or contain no microcrystalline to finely crystalline dolomite stratigraphic petrographical and sr isotopic data suggest that the ratner dolomite has formed penecontemporaneously from dense evaporitic seawater that percolated downward the distribution of the ratner dolomite is highly localized in the northern part of the study area suggesting that the downward flow of mg 2 rich fluids was restricted by interbedded anhydrite but where the fluids penetrated the underlying carbonate deposits were dolomitized the depletion in 18 o isotope varying from 4 5 to 6 6 pdb and the coarser and inhomogeneous textures of the ratner dolomite are considered to be the result of recrystallization which is interpreted to occur at elevated temperatures related to a thermal anomaly during the late devonian and carboniferous burial

microfabric analysis of mn carbonate laminae deposition and mn sulfide formation in the gotland deep baltic sea the manganese carbonate deposits of the anoxic littorina sediments of the gotland deep have been commonly related to the periodic renewal of deep water by inflowing saline water from the north sea the use of scanning electron microscopy based techniques allows identification of small scale sedimentary and geochemical features associated with mn carbonate laminae which has significant implications for models of mn carbonate formation varves occurring in the littorina sequence contain up to four laminae that may be placed in a seasonal cycle and kutnahorite laminae occur within varves only as a winter early spring deposit this kutnahorite laminae seasonality is in agreement with the seasonal distribution of major baltic inflow events recorded in historical records and a direct causal link between inflows and kutnahorite deposition is implied benthic foraminifera tests are found to be heavily encrusted in kutnahorite implying that benthic recolonization during oxidation events occurs concurrently with kutnahorite formation the relatively common occurrence of small 50 to 100 m hexagonal mn sulfide pseudomorphs associated with 13 of kutnahorite laminae studied is reported in gotland deep sediments for the first time although mn sulfide crystals are not usually preserved in the sediment the discovery of mn sulfide pseudomorphs suggests that initial formation of mn sulfide in the gotland deep may occur much more commonly during the process of kutnahorite formation than previous reports of mn sulfide occurrence have implied

mixing of siliciclastic and carbonate sediments in shallow shelf environments the inhibiting effect that siliciclastic material has on carbonate secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form however many modern and ancient shelf deposits contain a spectrum of sediments that are of mixed composition the processes responsible for this mixing can be grouped into four categories 1 punctuated mixing where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another 2 facies mixing where sediments are mixed along the diffuse boundaries between contrasting facies 3 in situ mixing where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates and 4 source mixing where admixtures are formed by the uplift and erosion of nearby carbonate source terranes the allochemical constituents of mixed sediments are both coralgal and foram mollusc in composition the foram mollusc assemblage is the most common because of the effects of increased turbidity unstable substrates and the clogging of filter feeding mechanisms associated with a siliciclastic influx

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

manganese authigenesis in the landsort deep baltic sea abstract manganese mineralogy because of its redox sensitivity is a valuable parameter for interpreting water column anoxia and sediment diagenesis in the baltic and especially the landsort deep the relatively widespread occurrence of mn carbonates and the unique observations of authigenic mn sulphides in sedimentary environments need to be accounted for within the models proposed for mn authigenesis in diverse settings in this study stratigraphic changes in the geochemistry and mineralogy are documented in two gravity cores using petrographic microscopy xrd sem eds analyses of c and s content 13 c isotopes icp ms cation determinations and electron microprobe element profiling the lamination in the bottom sediments of the landsort deep suggests essentially continuous anoxic conditions at the sediment surface during the last ca 4500 14 c years the most striking variations in the sediments are related to the occurrence of two mn ii precipitate rich sapropel intervals recent and 1390 1990 14 c years bp sapropel deposition is associated with relatively slow detrital sedimentation allowing the concentration of organic matter the sediment c org content is influenced by the variations in the primary production as well as the supply of terrestrial c org but a major control appears to be detrital dilution the precipitation of mn carbonate as individual aggregates of spherical particles dispersed within clayey sediment matrix and as laminae with semi seasonal cyclicity is believed to be largely induced by the high alkalinity in connection with organic matter deposition and degradation where h 2 s has exceeded fe availability mns has also precipitated most commonly as well developed hexagonal crystals but also as the cubic variety alabandite which has not previously been reported from a sedimentary environment an expansion of the anoxic bottom water conditions during sapropel deposition is interpreted by correlation with laminated intervals on the slope of the deep basin budget calculations for the supply of mn to the basin during mn rich sapropel formation can be better balanced by the addition of mn from dissolution of oxides formed prior to the anoxic expansion the importance of alkalinity for the precipitation of mn carbonates and sulphides does not exclude the need for considerable mn concentrations but the model argued in several recently published studies stressing mn availability as the major control does not seem appropriate for the landsort deep and may be too restrictive in many other settings as well

high resolution line scan analysis of resin embedded sediments using laser ablation inductively coupled plasma mass spectrometry la icp ms laser ablation inductively coupled plasma mass spectrometry la icp ms line scanning is a promising technique for producing high resolution m scale geochemical records on resin embedded sediments however this approach has not yet been thoroughly tested on sediment samples of known elemental compositions here we address this through the analysis of resin embedded quartz calcite and clay montmorillonite sediments spiked with al v mo and ba across a range of concentrations la icp ms spot analyses on these samples were compared to data independently obtained by conventional techniques solution nebulization icp optical emission spectroscopy sn icp oes sn icp ms and x ray fluorescence on fused glass beads data were reported as log ratios of the analyte elements normalized to ca si and al for calcite quartz and clay respectively to correct for varying ablation yields our la icp ms data demonstrate close agreement to within 6 of the reference values determined by the conventional techniques with high correlation coefficients r2 1 0 across the full range of concentrations and high precision 3 relative standard deviations after three repeated analyses barium was hosted in both aluminosilicates and carbonates in the clay matrix giving different yields elemental fractionation and leading to variable accuracy mean deviation of 15 a selection of the spiked sediments was used to produce artificial laminated sediments to further test the effects of line scanning on la icp ms accuracy and precision in resin embedded samples it appears that la icp ms line scan analyses have good accuracy deviations from the reference values generally 5 and high precision relative standard deviations of repeated analyses on the same sample generally 5 for our target elements moreover the la icp ms line scanning closely records the alternating geochemical profiles of our artificial laminations however calcium showed a clear tailing signal at the transition from a calcite to a quartz layer indicating that geochemical signals can be smeared at transitions to sediment layers devoid of analyte element s we also analyzed resin embedded natural sediments for comparison of la icp ms line scan data to parallel sub samples measured by sn icp oes and sn icp ms in general the results from la icp ms line scans of natural sediments correspond well with reference values and with high reproducibility corroborating the results of the artificial laminations the results for ca v mn sr mo ba and u in log ratios to al suggest that these elements can be analyzed semi quantitatively showing correlation coefficients r2 ranging from 0 59 to 0 85 compared to conventional analytical techniques however we show that using non matrix matched calibration standards such as nist srm 610 may induce deviations from the la icp ms values to the reference values consequently we recommend a simple protocol for further data correction in which binned mean la icp ms values are calibrated to a parallel series of discrete samples analyzed by these conventional techniques

mixed carbonates and siliciclastics in the quaternary of southern belize pleistocene turning points in reef development controlled by sea level change the belize barrier and atoll reefs represent one of the largest reef structures in the atlantic ocean the southern shelf of belize is a classic location of a modern mixed carbonate siliciclastic system whereas knowledge of the holocene deposits in the area is extensive data on the pleistocene system are fragmentary open questions include i the nature of the reef foundations carbonate versus siliciclastics ii the ages of the deposits including the initiation of the barrier reef and iii the response of the mixed system to sealevel fluctuations the results of a study of borings on the southern belize shelf are presented here six up to 105 m long borings were made to better understand the history of this important mixed system uranium series dating in the pleistocene was not possible because of diagenetic alteration however lithostratigraphy strontium isotopes and calcareous nannofossil biostratigraphy were used to constrain stratigraphic ages results support the contention that the quaternary development in belize was quite similar to that of other major barrier reefs such as the florida reef tract and further afield the great barrier and the new caledonian barrier reefs all of these barrier reefs are mixed carbonate siliciclastic systems and significant reef growth only began after the onset of high amplitude eccentricity controlled sea level changes and as late as during the exceptionally long and warm marine isotope stage 11 some 400 ka in belize early pleistocene sections at bases of borings include mollusc rich wackestones rare coral packstones and marls which were deposited under low to moderate energy conditions in a ramp setting before ca 900 ka during the high sea levels of marine isotope stage 25 and possibly earlier marine isotope stage 31 or 37 the belize shelf was subaerially exposed for most of the mid pleistocene and was dominated by siliciclastic sedimentation possibly during marine isotope stages 24 to 12 when highstands were comparatively low continuous reefs at the shelf margin were developing during highstands in the late pleistocene beginning with the long and high highstand of marine isotope stage 11 some 400 ka the southern shelf was flooded entirely and carbonates started to dominate once more reefs developed on top of siliciclastic deposits on the shelf a continuous barrier reef came into existence and largely developed on top of carbonates at the shelf margin during late pleistocene lowstands siliciclastics presumably no longer reached the shelf margin because of the topographic high of the barrier reef platform the quaternary belize example may serve as a model for reconstructing ancient mixed systems in icehouse worlds however any extrapolations are limited by the fact that fast growing scleractinian reef builders had not yet evolved in the palaeozoic

authigenic sulfide and carbonate mineral formation in holocene sediments of the baltic sea formation of authigenic sulfides and carbonates in holocene 14c dated sediments is interpreted based on analyses of cations fes s fes2 s corg and sulfur isotopes mineral distribution was studied in thin sections and mineral morphology with sem eds the sediments were deposited in the gotland deep baltic sea during freshwater and brackish stages calcium rich rhodochrosite mnco3 occurs in concentrations up to 17 dw in brackish water sediments and are mainly confined to 0 02 0 5 mm thick laminae the frequency with which these laminae occur suggests that they formed with a periodicity of one to a few years and their purity suggests that formation took place in a few weeks we propose that these carbonate laminae resulted from oxic water inflow to the euxinic basin mn ii dissolved in the water column was rapidly oxidized and large amounts of mn oxides reached the sediment reduction of these mn oxides in a high alkalinity environment facilitated rhodochrosite precipitation at the sediment surface pyrite in the brackish water sediments formed at or above the sediment water interface in an iron limited environment due to alternating oxic and euxinic conditions fes was oxidized resulting in a high fes2 sfes s ratio median 170 formation of iron sulfides in the freshwater sediments occurred below the sediment water interface in a sulfate limited environment as a result of the rapid exhaustion of reactive iron in the brackish water sediments excess h2s diffused downwards to pyritize the uppermost part of the underlying freshwater sediments

vivianite is a key sink for phosphorus in sediments of the landsort deep an intermittently anoxic deep basin in the baltic sea phosphorus p is an essential nutrient for marine organisms its burial in hypoxic and anoxic marine basins is still incompletely understood recent studies suggest that p can be sequestered in sediments of such basins as reduced iron fe p but the exact phase and the underlying mechanisms that lead to its formation are unknown in this study we investigated sediments from the deepest basin in the baltic sea the landsort deep site m0063 that were retrieved during the integrated ocean drilling project iodp baltic sea paleoenvironment expedition 347 the record comprises the whole brackish marine littorina sea stage including past intervals of extensive hypoxia in the baltic sea that occurred during the holocene thermal maximum htmhi and the medieval climate anomaly mca1hi and mca2hi various redox proxies e g the presence of laminations and high mo contents suggest almost permanent bottom water hypoxia during the littorina sea stage in the landsort deep the bottom waters were likely even seasonally anoxic or sulfidic during the mca1hi and mca2hi and permanently sulfidic during the htmhi with the use of micro analysis of sieved minerals sem eds xrd and synchrotron based xas we show that mn and mg rich vivianite crystals are present at various depths in the littorina sea sediments we also have indications for vivianite in the mca1hi mca2hi and htmhi deposits the formation of vivianite thus likely explains the high fe bound p fraction throughout the whole littorina sea stage shuttling of fe and mn from the shelves into the basin and high inputs of p in settling organic matter are likely key drivers for vivianite formation our study shows that vivianite can likely form in near surface sediments under a broad range of bottom water redox conditions varying from hypoxic and anoxic to sulfidic

internal anatomy of a mixed siliciclastic carbonate platform the late cenomanian mid turonian at the southern margin of the spanish central system the late cenomanian mid turonian succession in central spain is composed of siliciclastic and carbonate rocks deposited in a variety of coastal and marine shelf environments alluvial plain estuarine lagoon shoreface offshore hemipelagic and carbonate ramp three depositional sequences third order are recognized the atienza patones and el molar sequences the patones sequence contains five fourth order parasequence sets while a single parasequence set is recognized in the atienza and el molar sequences systems tracts can be recognized both in the sequences and parasequence sets the lowstand systems tracts only recognized for atienza and patones sequences are related to erosion and sequence boundary formation transgressive systems tracts are related to marine transgression and shoreface retreat the highstand systems tracts are related to shoreface extension and progradation and to carbonate production and ramp progradation sequences are bounded by erosion or emergence surfaces whose locations are supported by mineralogical analyses and suggest source area reactivation probably due to a fall in relative sea level transgressive surfaces are subordinate erosion and or omission surfaces with a landward facies shift interpreted as parasequence set boundaries the co existence of siliciclastic and carbonate sediments and environments occurred as facies mixing or as distinct facies belts along the basin mixed facies of coastal areas are composed of detrital quartz and clays derived from the hinterland and dolomite probably derived from bioclastic material siliciclastic flux to coastal areas is highly variable the maximum flux postdates relative sea level falls carbonate production in these areas may be constant but the final content is a function of changing inputs in terrigenous sediments and carbonate content diminishes through a dilution effect carbonate ramps were detached from the coastal system and separated by a fringe of offshore fine grained muds and silts as distinct facies belts the growth of carbonate ramp deposits was related to the highstand systems tracts of the fourth order parasequence sets during the growth of these ramps some sediment starvation occurred basinwards progradation and retrogradation of the different belts occur simultaneously suggesting a sea level control on sedimentation in the study area the co existence of carbonate and siliciclastic facies belts depended on the superimposition of different orders of relative sea level cycles and occurred mainly when the second order third order and fourth order cycles showed highstand conditions

pyrite with high mn content from the nankai trough formed from subduction induced cold seepage abstract pyrite and abundant calcite occur in a sandstone pipe collected from the eastern nankai trough electron microprobe analysis of the pyrite indicates that it contains appreciable amounts of manganese up to 1 5 mns 2 mole the present data and previous analytical data on pyrite indicate that manganese content of anoxic sedimentary pyrite is high but of hydrothermal pyrite very low in the pyrite studied here isomorphous substitution of manganese occurs stable isotope data on calcite coexisting with the pyrite as well as chemical data on the advecting fluids indicate that the advecting fluids are characterized by reducing conditions high concentrations of methane hydrogen sulfide and manganese and high mn fe ratios these characteristics could be responsible for the high manganese content of pyrite adsorption of manganese by a precursor iron sulfide may also be an important factor the present study demonstrates that the manganese content of pyrite is potentially a useful indicator of sedimentary and diagenetic processes and of the geological characteristics of ancient terrestrial sedimentary rocks

tracing bottom water redox conditions during deposition of lower and upper jurassic organic rich sedimentary rocks in the lusitanian basin portugal insights from inorganic geochemistry abstract the lower jurassic agua de madeiros am fm and vale das fontes vf fm formations and the upper jurassic cabacos formation cab fm are considered the most important units with petroleum source rock potential in the lusitanian basin and the likely sources for its widespread hydrocarbon occurrences nonetheless the bottom water redox conditions during their deposition remain debatable to resolve this controversy we investigated whole rock inorganic geochemical data of the most significant organic rich levels of the am vf and cab fms cropping out at basin scale significant variations in toc ts and redox sensitive elements contents and their ratios are evident within and between the organic rich levels of the studied units a positive covariation between primary productivity proxies toc enrichment and paleo redox proxies for the lower jurassic units clearly suggest an interdependence between enhanced primary productivity organic matter accumulation and bottom water redox conditions for the am fm the paleo redox proxies indicate that the black shales deposition took place beneath bottom waters that ranged from suboxic to strongly euxinic conditions with a clear predominance of the latter a toc threshold of 6 7 wt clearly separates samples deposited under suboxic to anoxic conditions from those deposited under true euxinic conditions and is interpreted as the minimum amount of organic matter om accumulation within sediments required to sustain h2s production at rates that outpaced its consumption through precipitation of sulphides and or om sulphurization allowing the diffusion of h2s to the bottom waters for the vale das fontes fm the paleo redox proxies suggest a prevalence of suboxic to anoxic bottom waters despite all black shales displaying toc contents greater than the above threshold the less reducing conditions relative to the am fm euxinic black shales are attributed to i a larger proportion of continental om ii lower reactivity of the om reaching the sediment water interface decreasing oxygen consumption and iii higher availability of reactive iron increasing the buffer effect to h2s produced through om remineralization by sulphate reducing bacteria both units display mo ef vs u ef covariation patterns that deviate from the field of sediments deposited under unrestricted open marine conditions towards higher mo enrichment relative to that of u indicating an accelerated transport of aqueous mo to the sediments consistent with the operation of a metal oxyhydroxide particulate shuttle linked to mn and fe redox cycling within the water column in a weakly restricted basin the mo cot regression line slope indicates a moderate degree of bottom water mass restriction with mo aq concentration of 60 70 of the present day seawater value and bottom water renewal times of 10 20 years akin to the present day cariaco basin the redox conditions of the cab fm organic rich levels are dependent on the location of the depositional environment in the basin with deposition taking place beneath oxygenated bottom waters at cabo mondego and under suboxic conditions at vale de ventos and pedrogao the latter denoting a larger degree of oxygen depletion than the former in this context the overall potential for om preservation should increase from cabo mondego to vale de ventos and pedrogao

siliciclastic foundations of quaternary reefs in the southernmost belize lagoon british honduras analyses of a closely spaced lattice of seismic profiles from the southernmost belize lagoon combined with logs of nearby drill holes reveal that the quaternary late pleistocene plus holocene reefs and carbonate sediments are growing on siliciclastic sediments which have an alluvial and delta like morphology the residual relief of these coastal plain deposits localized initial coral growth or an accumulation of calcareous skeletal material favored sites for these were elevations such as levees and bars of remnant channels and deltaic lobes

the manganese and iron shuttle in a modern euxinic basin and implications for molybdenum cycling at euxinic ocean margins a meaningful application of mo as a paleo redox proxy requires an understanding of mo cycling in modern reducing environments stagnant euxinic basins such as the black sea are generally regarded as model systems for understanding euxinic systems during early earth history however drawing direct parallels between the black sea and open marine euxinic margins is somewhat complicated by differences in the seawater residence time between these two environments we report sediment and pore water mo u mn and fe data for a euxinic basin with a short seawater residence time the weakly restricted gotland deep in the baltic sea here prolonged periods of euxinia alternate with brief inflow events during which well oxygenated saline water penetrates into the basin during these inflow events dissolved mn and fe that has accumulated within the euxinic deep water can be oxidized and precipitated co variations of mo and u within the sediment suggest that these inflow and oxygenation events may favor mo accumulation in the sediment through adsorption to freshly oxidized mn and fe solid phases once mo is sequestered within the deeper euxinic water and sediments mo retention can be further facilitated by conversion to thiomolybdate species and interactions with organic matter and metal sulfides by comparing our data with those from previous studies where a mn and fe shuttle for mo has been demonstrated we identify two prerequisites for the occurrence of this mechanism first there must be a water column oxic anoxic redox boundary this provides a solubility contrast for mn and fe second the residence time of seawater in the system has to be short weeks to a few years the latter criterion can be met through regular inflow in weakly restricted basins or upwelling in oxygen minimum zones at open marine continental margins based on prior work we suggest that similar conditions to those currently represented by the gotland deep may have prevailed at euxinic ocean margins during the proterozoic a boundary between euxinic and oxic water masses overlying the continental shelf may have resulted in accelerated mo transport through the water column with mn and fe oxyhydr oxides we propose that this mechanism along with mo isotope fractionation during adsorption could contribute to the light mo isotope composition observed in open marine euxinic sediment facies of the proterozoic

iron and manganese shuttles control the formation of authigenic phosphorus minerals in the euxinic basins of the baltic sea microanalysis of epoxy resin embedded sediments is used to demonstrate the presence of authigenic iron fe ii phosphates and manganese mn calcium ca carbonate phosphates in the deep euxinic basins of the baltic sea these minerals constitute major burial phases of phosphorus p in this area elevating the total p burial rate above that expected for a euxinic depositional environment particle shuttles of fe and mn oxides into the deep euxinic basins act as drivers for p bearing mineral authigenesis while fe ii phosphates are formed continuously in the upper sediments following the sulfidization of fe oxyhydroxides and release of associated p mn ca carbonate phosphates are formed intermittently following inflow events of oxygenated north sea water into the deep basins the mechanism of fe ii phosphate formation differs from previously reported occurrences of vivianite formation in marine sediments by occurring within rather than below the sulfate methane transition zone the spatial distribution of both authigenic phases in baltic sediments varies in accordance with the periodic expansion of anoxia on centennial to millennial timescales the results highlight the potential importance of authigenic p bearing minerals other than carbonate fluorapatite for total p burial in euxinic basins

lacustrine tight oil accumulation characteristics permian lucaogou formation in jimusaer sag junggar basin abstract the permian lucaogou formation of jimusaer sag in the southeast region of the junggar basin is a typical area recently attracting tight oil reservoir research efforts in china commercial oil has been obtained from many wells in this region the main lithological formation comprises thick mudstones two sweet spots exhibiting high porosity and permeability are interbedded in the mudstones the sweet spots comprise alternating thin layers of silt fine sandstones carbonatites and mudstones numerous core samples were analyzed to establish the hydrocarbon generation and storage potential of lucaogou formation s lithological units in this region the test results indicate that although the tight sandstones have a certain hydrocarbon generation potential mudstones are evidently higher quality source rocks the silt fine sandstones reservoir quality is best among the three rock types biomarker evidence shows the difference between the upper and the lower section lucaogou formation oil corresponding to the mudstone layer extracts within the upper and lower sweet spot respectively despite its thickness the thick bedded mudstone average thickness 80 m between the upper and lower sweet spots does not appear to contribute to the oil reservoirs since the distance between the thick mudstone and the sweet spot is quite large and the entire formation has generally low permeability migrating from the thick mudstone to the sweet spot is difficult hence oil in the sweet spots can be concluded to be from the adjacent mudstone to our knowledge this is the first study reporting this finding

uranium and molybdenum isotope systematics in modern euxinic basins case studies from the central baltic sea and the kyllaren fjord norway abstract recent investigations have revealed significant fractionation of 238u 235u between organic rich sediments of anoxic marginal seas and seawater indicating redox dependent u isotope fractionation this study explores the conditions controlling u isotope fractionation in selected modern anoxic basins baltic sea landsort and gotland deeps and the kyllaren fjord in norway and compares u with mo isotope fractionation therefore the concentrations and isotope compositions of dissolved u and mo from the water column and organic rich sediments from three currently anoxic basins have been analysed the water column samples from the kyllaren fjord display a moderate depletion of u and a strong depletion of mo with increasing depth these variations are associated with a decrease in 238u and an increase in 98mo with depth from 0 35 to 0 70 and from 2 4 to 2 6 respectively from the u isotope composition of the deep euxinic water column of the kyllaren fjord a minimum value of 238ured 0 7 for the u isotope fractionation during reduction is inferred due to the high sedimentation rate in the kyllaren fjord surface sediment samples are only moderately enriched in u and mo 4 g g and 6 g g to 37 g g respectively and display 238u and 98mo averages of 0 26 0 10 and 2 18 0 21 respectively water column samples from the baltic sea display a minor decrease in the u and mo concentrations and only negligible u and mo isotope fractionation compared to open seawater the sediment layers from the baltic sea landsort deep which were deposited under mostly anoxic conditions are moderately enriched in u up to 8 g g and highly enriched in mo up to 222 g g however u and mo isotopic compositions are significantly lighter with 238u of 0 36 0 08 and 98mo of 0 04 0 11 than those of typical organic rich sediments from anoxic basins these findings reveal that compared to mo the u isotopic composition of sediments in restricted and strongly euxinic basins like the kyllaren fjord is significantly more dependent on 1 the extent of u removal from the water column which is lower than that of mo and on 2 the sedimentation rate i e the fraction of authigenic u relative to detrital u in the sediment which is also lower compared to that of mo in more open and only temporarily euxinic basins such as the investigated basins of the baltic sea strong mo is coupled with weak u isotope fractionation between water and sediment these signatures were likely the result of isotope fractionation under weakly sulfidic conditions and the generation of isotopically light mo during frequently occurring flushing events with oxygen rich water from the open sea this implies that mo and u isotope signatures of sediments only record paleo water column redox conditions of restricted basins if the water column was permanently stratified

the effect of sea level and climate change on the development of a mixed siliciclastic carbonate deltaic coastline suwannee river florida u s a abstract florida s mixed siliciclastic carbonate northwest central gulf of mexico coastline is characterized by a 300 km long low energy sediment starved open marine marsh system fronted by a broad shallow limestone shelf the only significant point source of sediment to this system is the suwannee river which forms a small 20 km2 delta at the center of this coastline late pleistocene eolian dune formation along the suwannee river coastline reflects slightly drier conditions and local sediment sources influencing the early geologic development of this region as sea level rose in the early to middle holocene dunes on the low gradient shelf were transgressed and provided the core for the modern offshore sandy shoals with decelerating sea level rise in the middle to late holocene and probable increased riverine sediment input coastal sedimentation switched from transgressive to aggradational paleo distributary channels seaward of the delta coastline at approximately 4 000 cal yr bp indicate initial deltaic formation at this same time oyster reefs from the delta southward were able to keep pace with sea level rise and began to form large 20 km2 offshore oyster bioherms away from the river mouth the coastline continued to transgress until 2 350 cal yr bp to 1350 cal yr bp when the shoreline stabilized and the modern marsh system south and north of the river mouth respectively began to aggrade the geologic development of this coastline and the relict eolian dunes preserved within the modern marsh system indicates that middle to late holocene sea level did not exceed current elevations along this portion of the gulf of mexico coastline this finding agrees with other studies from the low gradient west central florida coast but contrasts with evidence for middle to late holocene highstands along other gulf of mexico shorelines

petrostratigraphic analysis of a late miocene mixed siliciclastic carbonate depositional system calabria southern italy implications for mediterranean paleogeography abstract mixed siliciclastic carbonate sediments are common in shallow water environments in which clastic deposition and carbonate production coexist in the mediterranean basin the tortonian messinian sedimentary successions are commonly comprised of marls alternations of marls with diatomites sands and sandstones limestones especially algal and coral reefs and evaporites most of the studies in the mediterranean basin have been focused on carbonate facies analysis whereas the siliciclastic portions are poorly described similarly to the other marginal settings of the mediterranean basin the capo vaticano area southern calabria southern italy experienced mixed sedimentation at that time petrological analysis was performed on 56 weakly cemented sandstones linking compositional signatures to stratigraphic data with the aim of investigating sedimentary response to the tortonian messinian transgression and its influence on the carbonate production the information obtained is used to refine the regional sediment dispersal pathways and paleogeography by means of bio stratigraphic evidence the studied succession to coeval mixed deposits dislocated in the mediterranean basin is correlated

grain size distributions of bed load inferences from flume experiments using heterogeneous sediment beds abstract the grain size fractions in the bedload transported over the five heterogeneous sediment beds of different values of bed roughness were computed from the flume experiments the existence of an entrapment factor associated with the sorting observed from the bed to active layer was modeled based on the modified critical shear stress to estimate the grain size fractions in the transport layer under given hydraulic conditions the efficiency of these models was tested with the observed data subsequently the patterns of observed grain size distributions in the transport layer were tested to identify the distributions developed in the active layer due to sorting using three probability density functions pdf such as log normal log hyperbolic and log skew laplace tests indicated that a log skew laplace distribution fitted best for 49 a log hyperbolic for 31 and a log normal for 20 out of forty five bedload samples collected under unidirectional flow with changes in flow discharge and bed roughness the results of this study would be useful to specify the grain size distributions in the bedload formed under different hydrodynamic conditions in various sedimentary environments

recycling of manganese from anoxic sediments in stagnant basins by seawater inflow a study of surface sediments from the gotland basin baltic sea abstract the occurrence of mn carbonates in sapropelic sediments has been proposed to indicate that the host sediment originally accumulated under oxygenated bottomwaters in the central baltic sea ca rich rhodochrosite layers in sapropelic sediments have been related to inflows of oxic seawater from the north sea into the brackish predominantly anoxic deeps of the central baltic this study attempts to verify the model of authigenic mn carbonate formation by comparing oceanographic records directly with the composition of surficial sediments of the gotland basin surface sediments of the gotland deep sampled in 1997 displayed significant ca rich rhodochrosite enrichments at 6 5 11 and 15 cm sediment depth which reflect periods of intense seawater inflows in 1969 76 1948 56 and 1931 39 respectively however the latest major seawater inflow detected in 1993 was not reflected in the surface sediment the topmost 6 cm of the sediment was totally depleted in mn and 210pb data implied a disturbed top layer down to 5 cm calculations of saturation indices indicate that the porewaters were undersaturated with respect to mn and ca carbonate phases in the uppermost 8 cm in 1997 at greater depths the porewaters were close to equilibrium with respect to calcite and rhodochrosite the ca rhodochrosite layers corresponded well to a sediment core sampled at the same location in 1994 but that core displayed a further enrichment of ca rich rhodochrosite close to the sediment surface which can be related to a major inflow of north sea water in 1993 the significant decrease of about 2 3 mol m2 mn in the uppermost 6 cm of a disturbed sediment surface from 1994 to 1997 corresponds to an enrichment of about 20 mol l of dissolved mn within the 90 m thick anoxic water column in 1997 we conclude that several inflows of dense seawater into the gotland deep monitored between 1994 and 1997 led to a resuspension of the unstable fluffy surface sediment layer authigenic ca rich rhodochrosite which had formed immediately after the major inflow of oxic seawater in 1993 was therefore redissolved in undersaturated bottomwaters and mn was recycled from surficial sediments into the water column this in turn means that in contrast to the established model of ca rhodochrosite formation as a result of seawater inflow the occurrence of mixed mn depleted layers does not prove that seawater inflow has not occurred during the deposition of these sediments

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

facies architecture of the mixed carbonate siliciclastic inner continental shelf of west central florida implications for holocene barrier development abstract sediment vibracores and surface samples were collected from the mixed carbonate siliciclastic inner shelf of west central florida in an effort to determine the three dimensional facies architecture and holocene geologic development of the coastal barrier island and adjacent shallow marine environments the unconsolidated sediment veneer is thin generally

spatial extent and degree of oxygen depletion in the deep proto north atlantic basin during oceanic anoxic event 2 massive organic matter burial due to widespread ocean anoxia across the cenomanian turonian boundary event 94 ma resulted in a major perturbation of the global carbon cycle the so called oceanic anoxic event 2 oae2 the characteristics and spatial distribution of the oae2 deposits that formed in the deep basin of the proto north atlantic remain poorly described however here we present proxy data of redox sensitive trace elements e g mo fe al corg ptot and mn for oae2 sediments from five deep sea drilling project and ocean drilling program sites located in the deep proto north atlantic basin our results highlight that bottom waters in the entire deep proto north atlantic were anoxic during most of oae2 furthermore regressions of mo with total organic carbon content toc previously shown to document the degree of water mass restriction confirm that the water circulation in the proto north atlantic basin was severely restricted during oae2 comparison of these values to mo toc ratios in the present day black sea suggests a renewal frequency of the deep proto north atlantic water mass of between 0 5 and 4 ka compared to a maximum of 200 years for the present day northern atlantic the plenus cold event a cooler episode during the early stages of oae2 hypothesized to be caused by declining pco2 due to extensive burial of organic matter appears to have led to temporary re oxygenation of the bottom water in the deep proto north atlantic basin during oae2

storm generated sedimentary structures in subtidal marine facies with examples from the middle and upper ordovician of southwestern virginia abstract the role of storms is of major importance in forming stratification in open shelf facies though storm processes on modern shelves are not fully understood enough is known to see how sediments are influenced storms transport sand away from coastal areas and suspend and transport sand and mud on the open shelf when wave base is lowered storms generate winnowed lag deposits of shells or gravel but coarser sediment and shells of megafauna are little transported except in very near shore environments the martinsburg formation middle and upper ordovician of southwestern virginia was deposited on a storm influenced open marine platform in contrast to the classic turbidite flysch basin of the martinsburg in the great valley of virginia to the northeast deposition of most martinsburg sediments was due to storms sediments deposited during single storm events occur in characteristic fining upward sequences 1 to 80 cm thick in both carbonate and terrigenous clastic dominated areas of the platform individual storm deposits consist of a sharp erosional base overlain by a couplet of whole fossil packstone and laminated calcarenite siltite or quartzose siltstone to very fine sandstone which is gradational to shale packstones are typically intraclastic have shells aligned parallel o bedding and convex up often with adhering or contained mud and have abundant infiltration textures such as cement filled shelter voids packstones grade abruptly to a laminated bed with horizontal plane lamination large and small scale in phase undulatory lamination and wave ripple cross lamination commonly occurring in ordered vertical sequences laminated beds contain escape burrows are weekly graded and have irregularly mounded upper bed surfaces laminated beds grade upward to shale containing horizontal branching burrows and marine fossils the faunal content of the fining upward sequences matches that of the interbedded shale storm generated beds vary greatly in thickness laterally and frequently pinch out completely fining upward sequences formed by scouring winnowing and suspension of the sand and mud during the height of the storm to form the erosional base and autochthonous lag of whole fossils storms preferentially preserve whole fossils rather than fragmenting them infiltration of finer sediment into the lag deposit and deposition of the laminated bed occurred as the storm waned laminated beds are molded into a distinctive suite of sedimentary structures by wave generated currents the shale represents deposition of finest storm suspended material and continued hemipelagic sedimentation similar sequences are widely distributed in the geologic record variability of storm generated sequences can be related to changing water depth thus storm deposits may be useful in basin analysis to estimate relative water depths and trace transgressive and regressive events

manganese accumulation and solid phase speciation in a 3 5 m thick mud sequence from the estuary of an acidic and mn rich creek northern baltic sea in sediments manganese mn is typically enriched in the form of authigenic mn hydroxides at the water sediment interface where intensive redox cycling of mn occurs here we show based on existin

mixed carbonate siliciclastic sedimentation on a tectonically active margin example from the pliocene of baja california sur mexico bioclast rich coarse grained deposits in the pliocene loreto basin provide a record of mixed carbonate and siliciclastic sedimentation at the steep hanging wall margin of this small fault controlled basin sedimentary facies consist of sand to gravel sized carbonate debris mixed with volcaniclastic sand and gravel in a proximal to distal facies tract that includes matrix rich and matrix poor shelly conglomerate impure calcirudite and calcarenite mixed composition turbidites and bioturbated calcarenitic sandstone carbonate material was produced by mollusks and other benthic organisms on a narrow high energy shelf and mixed with volcaniclastic sand and gravel in cross shelf channels these mixtures were transported down a steep subaqueous slope by debris flows grain flows and turbidity currents forming foresets and bottomsets of marine gilbert type deltas this style of mixed carbonate siliciclastic sedimentation has not been documented in detail elsewhere but should be locally abundant in the stratigraphic record of fault bounded basins particularly those with cool or nutrient rich waters that support relatively few binding and framework building faunas recognition of similar facies in other settings can provide useful insights into ancient conditions of carbonate production oceanography climate and tectonics

cyclic sedimentation in the mixed siliciclastic carbonate abo hueco transitional zone lower permian southwestern new mexico abstract in southwestern new mexico lower permian wolfcampian rocks grade southward from nonmarine siliciclastics abo and earp formations to marine carbonates hueco and horquilla formations a transitional zone between siliciclastic and carbonate facies trends east northeast across southwestern new mexico and consists of 64 to 186 m of cyclically interbedded siliciclastic and carbonate rocks which were deposited in tidal flat and shallow marine environments shallow marine facies include fossiliferous limestone and olive gray shale tidal flat facies consist of 1 ripple laminated sandstone which was deposited on intertidal sandflats near mean low tide 2 mixed sandstone shale which was deposited on an intertidal flat shoreward of the ripple laminated sandstone facies and 3 nodula shale which is characterized by pedogenic calcareous nodules and was deposited in a supratidal setting the intertidal facies are truncated by or grade laterally into rare channel sandstones which represent tidal creek or estuarine facies in addition to siliciclastic tidal flat deposits a few beds of laminated carbonate also were deposited in the intertidal zone vertical sequence analysis aids in delineating three types of depositional cycles asymmetrical cycles display the vertical sequence basal fossiliferous limestone olive gray shale ripple laminated sandstone mixed sandstone shale nodular shale and record shoreline progradation the asymmetrical cycle is always overlain by fossiliferous limestone which indicates a major transgression that inhibited siliciclastic sedimentation a common symmetrical cycle consists of fossiliferous limestone olive gray shale ripple laminated sandstone olive gray shale fossiliferous limestone and indicates systematic seaward and landward migration of facies zones associated with small scale sea level changes a less common symmetrical cycle involves laminated carbonate fossiliferous limestone aminated carbonate cyclic sedimentation in abo hueco transitional strata is most likely the result of glacial eustatic sea level fluctuations

first occurrence and stable isotope composition of authigenic γ mns in the central gotland deep baltic sea the occurrence of authigenic mns in organic matter rich sediments of the central gotland deep is reported for the first time the hexagonal manganese sulfide was found in a thin sediment layer with an approximate age of 1130 years and has an isotopic composition of 34s 13 vs v cdt this indicates that the bonded sulfur is derived from the anaerobic microbial reduction of pore water sulfate sem analysis reveals that mns occurs as idiomorphic crystals of about 200 m length and 150 m width much larger than the diameters of co existing calcian rhodochrosite globules 6 m it is suggested that formation of mns took place in a diagenetic environment which was locally free from reactive iron

characteristics and formation mechanism of multi source mixed sedimentary rocks in a saline lake a case study of the permian lucaogou formation in the jimusaer sag northwest china abstract the permian lucaogou formation in the jimusaer sag of the southeastern junggar basin in china is an uncommon set of mixed sedimentary rocks the mixed sediment content of the lucaogou formation is unusual due to the large amounts of tuffaceous material which makes the system more complex than the commonly mixed siliciclastic carbonate rocks in this study the volcanic material acts as a third end member component in a multi source mixed sedimentary system therefore a new type of mixed siliciclastic carbonate tuffaceous rocks has been introduced methods including core observations thin section analysis grain size measurements and x ray diffraction are used to investigate the characteristics of mineral components sedimentary structures and lithological assemblages in upper and lower sections of the formation these analyses are then used to determine the lateral distribution area of mixed sedimentation sedimentary mixing processes originally described for siliciclastic carbonate systems are used and expanded here for the multi source mixed rocks in a saline lacustrine basin controlling factors on mixed sedimentation included climate change lake level fluctuation tectonic activity and sediment supply rate mentioned in previous studies as well as variations of energy levels in different parts of the lake mixed depositional models for the lower and upper sections of the lucaogou formation in saline lacustrine basin have been established respectively

early diagenesis of foraminiferal calcite under anoxic conditions a case study from the landsort deep baltic sea iodp site m0063 abstract the chemical composition of foraminiferal calcite is widely used for studying past environmental conditions and biogeochemistry however high rates of microbial organic matter degradation and abundant dissolved metal sources in sediments and pore waters may impede the application of foraminifera based proxies due to formation of secondary carbonates or other authigenic minerals on and or inside of foraminiferal tests secondary carbonate precipitation severely alters the bulk foraminiferal geochemistry and can be difficult to eliminate through standard foraminiferal trace element cleaning procedures we present results showing the mineral composition and formation sequence of diagenetic coatings on foraminiferal tests formed under extreme anoxic conditions in the baltic sea s deepest basin the landsort deep iodp exp 347 site m0063 our study focuses primarily on the diagenetic carbonates present on and in the tests of the low oxygen tolerant benthic foraminiferal species elphidium selseyensis and elphidium clavatum we applied various geochemical and imaging methods to ascertain the diagenesis processes and the authigenic mineral formation sequence on foraminifera the authigenic carbonates were enriched in mn mg fe and ba depending on the environmental redox conditions when the authigenic carbonates were precipitated concentrations of redox sensitive elements such as mn and fe were particularly elevated in bottom waters and sedimentary pore waters under oxygen depleted conditions in the landsort deep resulting in formation of carbonates with highly elevated mn and fe contents in addition to mn and fe carbonates several other types of authigenic minerals also formed on and in the foraminiferal chambers including authigenic calcite and non carbonate accessory minerals the formation sequence reveals the redox sensitivities of different elements and the preferential sequence of oxidants used by the microbes during organic matter oxidation and secondary redox reactions this study provides a case study of extreme early diagenesis of foraminiferal calcite and may serve as a valuable guide when interpreting foraminiferal trace element records from low oxygen environments

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

sea level control of mixed carbonate siliciclastic gravity flow deposition lower part of the keeler canyon formation pennsylvanian southeastern california depositional cycles present in a mixed carbonate and quartz gravity flow sequence exposed in the death valley owens valley of southeastern california may record the response of this system to third order 0 7 1 4 m y sea level changes during late pennsylvanian time time equivalent outer shelf and basin margin deposits elucidate the following key elements of this depositional system 1 a distally steepened ramp profile 2 an unchanneled basin margin sequence which accumulated as a line sourced apron system and 3 penecontemporaneous deposition of carbonate and fine grained quartz sediment in both the shallow and deep water regimes basin margin facies consist of mudstones turbidites debris flows and megabreccias organized into thickening and coarsening upward packages lime mudstone intervals 3 7 m thick alternate with mixed carbonate siliciclastic gravity flow intervals 10 30 m thick time equivalent outer ramp facies show a similar organization of alternating silty bioclastic wackestones grainstones 10 40 m thick containing a diverse open marine fauna and rhythmically bedded lime mudstone 15 60 m thick which is barren of fauna an upward increase in debris flows and megabreccias within basin margin cycles indicates the involvement of large scale ramp processes and cannot be explained by simple progradation and abandonment of depositional lobes the absence of megabreccia caps on many of the cycles argues against autocyclic progradation and collapse of the platform although larger scale coarsening and thickening upward trends within the basin margin succession are attributed to autocyclic processes instead we propose that cycles develop in both the shallow and deep water regimes by changes in relative sea level drowning of the outer shelf during relative highstands rhythmically bedded lime mud stone would yield starved basin deposits lime mudstone as sea level falls both carbonates and siliciclastics prograde closer to the shelf edge silty bioclastic wackestones grainstones thus activating the mass transport system mixed clastic gravity flow packages increased storm and wave influence on the outer ramp upper slope triggers debris flows and occasional large scale collapses producing megabreccias most models of turbidite deposition have stressed reciprocal sedimentation with sea level change bioclastic turbidites during highstands and silicilclastic turbidites during lowstands instead our model for mixed clastic deposition emphasizes the importance of the build up profile the position of sea level relative to the shelf margin and the rate of change of sea level

redox dependent changes in manganese speciation in baltic sea sediments from the holocene thermal maximum an exafs xanes and la icp ms study manganese mn enrichments in sediments of the deep basins of the baltic sea are believed to consist of ca mn carbonates that form from mn oxides following periodic inflows of oxygen rich north sea waters however a range of mn bearing mineral phases that besides mn carbonates e g ca rhodochrosite can include mn sulfides are known to be present in marine sediments with formation mechanisms that are sensitive to redox conditions in this study we use high resolution synchrotron exafs and xanes combined with la icp ms and micro xrf to investigate the nature of the mn enrichments in sediments from the holocene thermal maximum approx 8000 4000 cal yr bp at a site in the northern gotland basin analyses were performed on epoxy embedded sediment sequences we specifically address the role of changes in redox conditions in bottom waters as inferred from sediment molybdenum mo contents for mn sequestration we find that an up core increase in mo indicating a transition into more anoxic and sulfidic euxinic bottom water conditions is accompanied by a decline in total sediment mn contents while mn carbonates dominate the mn mineral fraction in the low mo interval in the more sulfidic high mo interval mn is associated with framboidal pyrite mn fe ratios in the sulfidic interval vary between the investigated sequences but reach values of up to 7 7 mol this exceeds ratios previously reported for sedimentary pyrite and exafs spectra indicate that sulfide bound mn is predominately tetrahedrally coordinated when mn fe ratios are high this suggests that mn is incorporated in other fe s phases such as mackinawite besides pyrite there is also evidence for the presence of a low concentration of mn associated with detrital aluminosilicates throughout the investigated intervals our results suggest that increased bottom water euxinia inhibited the formation of mn carbonate at this site during the holocene thermal maximum possibly due to a more rapid reduction of mn oxides in more sulfidic bottom waters c 2014 elsevier b v all rights reserved less

development of anoxia during the holocene fresh brackish water transition in the baltic sea one of the most pronounced environmental changes during the holocene baltic sea history was the transition from the freshwater ancylus lake to the brackish water litorina sea the establishment of

dissolution and its impacts on reservoir formation in moderately to deeply buried strata of mixed siliciclastic carbonate sediments northwestern qaidam basin northwest china abstract petroleum exploration is increasingly extending from shallowly to moderately to deeply buried strata with reservoir quality being a key the formation mechanism of conventional clastic and carbonate reservoirs under such conditions has been widely investigated however the mechanism of mixed siliciclastic carbonate reservoirs has not been well studied in this paper we address this issue using a case study in the northwestern qaidam basin northwest china n1 e1 2 age 2500 4500 m dissolution pores and fractures dominate the reservoirs however only the fractures were the focus of previous studies thus here we investigate dissolution and its impacts on reservoir formation providing a complementary understanding of the reservoir formation in the basin using core observations and examining thin section it was discovered that dissolution was both random and followed bedding the dissolved components primarily included calcareous and gypsum minerals with fingerprints that are characteristic of burial dissolution further electron probe analysis on authigenic minerals revealed that the dissolution fluid might have originated from acidic formation fluids associated with hydrocarbon generation the fluids passed through faults and fractures dissolution pores were an important component of the reservoir providing approximately 60 of the porosity in addition segments of high porosity generally above 5 are associated with dissolution based on these observations a schematic model was established to explain the impacts of dissolution on reservoir formation specifically organic acidic formation fluids enter tectonic fractures resulting in dissolution as they pass through them this dissolution enhances the size of the pore space and the reservoir properties of the rocks eventually developing a fracture dissolution reservoir

formation and solid solution behavior of ca rhodochrosites in marine muds of the baltic deeps authigenic ca rhodochrosites are found in organic rich sediments in the deep anoxic basins of the baltic sea rhodochrosite formation is apparently the result of organic matter degradation the rhodochrosite contains 10 to 40 mol caco3 and 2 to 5 mol mgco3 as determined by microprobe the composition of the carbonates at a given depth varies by about 5 mol mnco3 sem revealed the rhodochrosite to be present as globular aggregates consisting of microcrystallites dissolution features such as cavities within the aggregates are frequently observed and indicate that extensive recrystallization takes place pore waters are greatly supersaturated with respect to both rhodochrosite and calcite rhodochrosite is only found in sediments where pore waters show the highest degree of supersaturation due to ion exchange ca2 diffuses from the underlying freshwater clays this results in increasing aca2 amn2 ratios in the pore waters from the sediment surface downward in response to this the maximum caco3mnco3 ratio also increases with depth the composition of rhodochrosite which forms under these conditions may be determined by both the porewater aca2 amn2 and precipitation kinetics however if their composition is controlled solely by the aca2 amn2 in solution their behavior can be described by a regular solid solution model

geochemical characterization of a marine sediment core from the joides basin ross sea antarctica abstract the chemical fractionation of ten metals al ti cr fe cd cu mn pb zn and ni is reported for a marine sediment collected in the joides basin ross sea antarctica to evaluate their mobility and availability the bcr sequential extraction procedure was applied on 11 sections of the sediment the analyses performed both by icp oes and gf aas highlighted that most of the elements were in the residual phase showing a strong binding with the matrix and a low availability the bcr sequential procedure allowed us to have an insight into the chemical properties of the sediment and provided useful information about the redox state of the sediment itself and important indication on the availability and partitioning of different metals a chemometric treatment was applied on the dataset and it showed a separation between the superficial and the deep sections of the core the first being more influenced by the presence of mn and the second by an increase in al ti fe cr and pb concentrations

holocene history of the baltic sea as recorded in a sediment core from the gotland deep a 4 m long sediment core from the gotland deep baltic sea was investigated by means of biostratigraphical and chemical parameters and c 14 datings this multidisciplinary approach allows us to ev

on the causes for salinity variations in the baltic sea during the last 8500 years 1 the baltic sea became connected to the open sea about 8500 years b p and that marked the beginning of the still continuing litorina sea stage there have since been significant long term variations of the salinity from a maximum of some 10 15 to the present of 7 8 the salinity variations have been known since the beginning of the twentieth century and various mechanisms have been proposed to explain these however so far no one has actually tried to quantify and thereby rank the relative importance of the different proposed mechanisms in this paper we used a simple oceanographic model to quantify the impact of changes in cross sectional areas of the inlets to the baltic we found that such changes cannot explain the full variation of the salinity we propose that the remaining salinity variations 0 5 5 are explained by changes in net freshwater input in the range 15 60 the calculated variations in the freshwater supply are in large coherent with known variations of the northern european climate we show that other possible factors as increased mixing frontal displacements higher deep water salinity and larger depths in kattegat and larger oscillating flows across the sills due to increased sea level variability are less likely to have made substantial contributions to the salinity variations in the baltic sea

the geochemistry of manganese carbonate in panama basin sediments abstract the mn distribution in panama basin area sediments and interstitial waters is discussed striking surficial mn enrichments produced by a well known diagenetic recycling process characterize the sediments of the region thermodynamic solubility calculations indicate that in at least one core interstitial waters approach saturation with respect to mnco3 a mixed carbonate phase of composition mn48 ca47 mg5 co3 was recovered from an ash band in the same core the association of this material with the coarse volcaniclastic debris is thought to result from facile manganous carbonate precipitation in sediment horizons of coarser mean grain size since sulphate reduction in the upper two metres of panama basin sediments is fairly minor little increase in alkalinity is observed and it is postulated that significant production of carbonate alkalinity is not a prerequisite for manganous carbonate generation in hemipelagic sediments a more important factor appears to be the availability of mn oxides for solution during early diagenesis stable c isotopic analyses indicate that little c of organic origin is used in the precipitation reaction in either panama basin or loch fyne scotland sediments

origin and environment of manganese rich sediments within black shale basins abstract sediments with unusually high manganese contents occur in anoxic basins of the central baltic sea we present a new model for the enrichment of manganese which is based on sedimentological and geochemical analyses of holocene sediments from the gotland deep and on published hydrographic data due to salinity stratification and high primary production bottom waters of the central baltic sea are anoxic and rich in dissolved mn 2 episodically bottom waters become oxygenated by inflows of denser water from the north sea mixing results in oxidation of mn 2 to fine grained particulate oxides which accumulate in the deepest parts of the basins where currents are mostly absent here anoxic conditions are re established within a few months or years and manganese oxides are again dissolved causing high concentrations of mn 2 in the near bottom layer alkalinity is high as a consequence of bacterial reduction of manganese oxides and sulphate under these conditions manganese is reprecipitated and forms a layer of ca rich rhodochrosite on the top of laminated sapropels occasionally periods of such extremely and rapidly changing redox conditions are followed by long term oxygenation of bottom waters in that case a layer rich in manganese oxides forms on the top of a bioturbated layer due to dissolution of rhodochrosite and oxidation of manganese in the near surface sediment return of anoxic conditions results again in the transformation of manganese oxides into rhodochrosite varying rhodochrosite contents in the basinal sediments therefore record a detailed history of redox conditions in bottom waters the manganese rich sediments of the baltic sea share many features with some occurrences of lower jurassic and lower carboniferous manganese ores in western and central europe we therefore suggest that these manganese enrichments were formed by similar processes

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

cyclic sedimentation of carbonate and siliciclastic deposits on a late precambrian ramp the elisabeth bjerg formation eleonore bay supergroup east greenland abstract the 300 m thick upper precambrian elisabeth bjerg formation in east greenland represents a period of intermittent siliciclastic dominated marine deposition on a carbonate ramp four depositional systems are identified within the exposed formation 1 a siliciclastic ramp system formed by prograding shoreface or delta complexes 2 a carbonate outer ramp system comprising rhythmically interbedded carbonate mudstone subtidal stromatolitic biostromes calcarenite deposits and siliciclastic mudstone 3 a transitional siliciclastic carbonate system consisting of 0 3 0 6 m thick subtidal rhythmites created by carbonate mudstone and conglomerates alternating with siliciclastic mudstone and 4 a carbonate inner ramp system consisting of intertidal and subtidal channel deposits on th basis of stacking patterns within the depositional systems lowstand transgressive and highstand systems tracts can be inferred which are traceable across the entire outcrop area more than 200 km along and 100 km perpendicular to basin strike the systems tracts combine to form five 30 100 m thick sequences within the elisabeth bjerg formation and two that extend into the surrounding formations all of the sequences show the same basic internal architecture most likely developed in response to third order glacio eustatic changes in sea level the paleogeographic evolution and the response of the four depositional systems to cyclic changes in sea level are interpreted using a ramp to basin model during lowstands sedimentation was dominated by siliciclastic deposition stranded lowstand shoreline deposits were formed in the more distal part of the ramp while the inner part of the ramp was a zone of sediment bypass during subsequent relative sealevel rise the ramp was flooded and starved of sediment early highstands were characterized by carbonate deposition including the formation of large stromatolite buildups while siliciclastic deposition was confined to a narrow near coastal zone during late highstands decreasing accommodation space resulted in progradation of the siliciclastic deposits forcing carbonate depos tion basinward

mixed siliciclastic carbonate shelf sedimentation lower devonian sequences of the sw anti atlas morocco abstract in the south western anti atlas of morocco dra plain a continuous exposure of lower devonian sedimentary successions more than 400 km long provides an example of mixed siliciclastic carbonate shelf sequences the carbonates were deposited adjacent and down dip to large lobes of storm dominated deltaic complexes during sea level lowstands and subsequently transgressed over the 200 m thick prograding siliciclastic wedges during sea level rise depositing limestone units between 5 and 20 m thick the deltaic lobes switched through time and caused alternating siliciclastic supply along the shoreline oblique parallel transect condensed limestone successions formed in clastic sediment starved areas due to delta complex abandonment down gradient in outer ramp environments the direct juxtaposition of carbonate and siliciclastic lithofacies associations comprising rhythmic lime mudstones marls and massive shelf sandstones provides the opportunity for mutual interpretation of their mode of deposition and bathymetry this lateral relationship suggests that significant amalgamation took place in falling stage systems tracts to produce laterally extensive shelf sandstone sheets on the outer ramp two types of stacking patterns are observed in prograding siliciclastic wedges a normal progradational shoreline pattern with well developed parasequence sets in the proximal ramp and an abrupt regressive succession in which the amalgamated shelf sandstones rest more or less directly on offshore siltstones in the distal ramp in the latter case the falling stage systems tract sandstones are overlain by a relatively thick cyclic alternation with brachiopod rich storm beds below a marked transgressive surface at the base of the capping transgressive limestones the cyclic alternation is interpreted as lowstand systems tract deposits marked flooding surfaces on parasequence sets are fe enriched and contain abundant articulated brachiopods indicating breaks in sedimentation and an overall deepening upward facies from the underlying maximum regression and sequence boundary these aggradational to retrogradational stacked lowstand systems tracts are thus rather transgressive not regressive in character as is commonly described in sequence stratigraphic ramp models

the behavior of redox sensitive metals across a laminated massive laminated transition in saanich inlet british columbia abstract holocene laminated sediments in saanich inlet british columbia are interrupted by frequent non laminated massive layers these layers may be debris flows released by earthquakes or bioturbated sediments deposited during periods of relatively high bottom water oxygen concentration and or low surface productivity or both we determined the organic carbon content and the concentration of a suite of redox sensitive metals in bulk sediments at approximately 1 cm resolution across a laminated massive laminated interval odp leg 169s site 1033 hole b 4h4 54 74 cm to determine the redox conditions under which the massive layer was deposited our results indicate that this massive interval was deposited under anoxic bottom waters manganese al ratios are consistently low throughout the massive section while mo al cd al re al and u al ratios are enriched relative to their metal al ratios in detrital material represented by cowichan river suspended sediments the concentration of organic carbon in the lower portion of the massive layer is higher than in the upper portion which has a concentration similar to that in the overlying and underlying laminated sediments well defined peaks in mo al cd al and re al and a broad peak in u al occur in the lower portion of the massive layer the positions of the cd al re al and mo al peaks as well as the increase in organic carbon content with depth in the massive layer are best explained by a process of diagenetic redistribution of metals that occurred after the massive layer was emplaced

sediment transport patterns determined from grain size parameters overview and state of the art abstract grain size trends have been applied in many diverse sedimentary environments to determine sediment transport paths generally coinciding with information from tracer studies current measurements and the orientation of sedimentary structures the different methods proposed to date are critically analysed and compared with reference to recent field studies it is concluded that the two dimensional methods produce comparable results and may in fact complement each other in spite of the advances several problems still exist which include the sampling method and density the choice of trend types the relative weight of grain size parameters and the interpretation of results these are discussed together with possible solutions

grain size analysis of the lower cambrian lower cretaceous clastic sequence of jordan sedimentological and paleo hydrodynamical implications abstract 356 sand sized samples ranging in age from early cambrian epoch to late cretaceous epoch of known depositional environments were analyzed mechanically to obtain the grain size parameters of mode median mean and sorting the constructed grain size distribution curves for the various paleozoic and mesozoic formations were interpreted in terms of the paleo hydrodynamic processes prevailing through transportation and deposition the study proved that the grain size parameters of sand sized sediments most sensitive to paleo depositional environmental recognition were the graphic mean grain size and the inclusive graphic sorting mean grain size values below 1 77 of a sand sized sample could indicate a fluvial channel paleo depositional environment whereas the mean grain size values above 2 8 are indicative to a shallow marine paleo depositional environment sorting values above 1 1 may indicate a fluvial channel paleo depositional environment a bivariate discriminatory plot of mean grain size versus sorting yields two fields that can successfully discriminate between the fluvial channel paleo depositional environment and the shallow marine paleo depositional environment a new grain size parameter termed the mean sorting index was introduced in this study and calculated by dividing the mean grain size value over the sorting value it is recorded here that the mean sorting index is more sensitive to paleo depositional environment recognition than the individual mean grain size and sorting parameters

hypoxia driven variations in iron and manganese shuttling in the baltic sea over the past 8 kyr the baltic sea has experienced three major intervals of bottom water hypoxia following the intrusion of seawater circa 8 kyr ago these intervals occurred during the holocene thermal maximum htm medieval climate anomaly mca and during recent decades here we show that sequestration of both fe and mn in baltic sea sediments generally increases with water depth and we attribute this to shelf to basin transfer shuttling of fe and mn burial of mn in slope and basin sediments was enhanced following the lake brackish marine transition at the beginning of the hypoxic interval during the htm during hypoxic intervals shelf to basin transfer of fe was generally enhanced but that of mn was reduced however intensification of hypoxia within hypoxic intervals led to decreased burial of both mn and fe in deep basin sediments this implies a nonlinearity in shelf fe release upon expanding hypoxia with initial enhanced fe release relative to oxic conditions followed by increased retention in shelf sediments likely in the form of iron sulfide minerals for mn extended hypoxia leads to more limited sequestration as mn carbonate in deep basin sediments presumably because of more rapid reduction of mn oxides formed after inflows and subsequent escape of dissolved mn to the overlying water our fe records suggest that modern baltic sea hypoxia is more widespread than in the past furthermore hypoxia driven variations in shelf to basin transfer of fe may have impacted the dynamics of p and sulfide in the baltic sea thus providing potential feedbacks on the further development of hypoxia

manganese and iron geochemistry in sediments underlying the redox stratified fayetteville green lake abstract manganese and iron are redox sensitive elements that yield clues about biogeochemistry and redox conditions both in modern environments and in the geologic past here we investigated mn and fe bearing minerals preserved in basin sediments underlying fayetteville green lake a redox stratified lake that serves as a geochemical analogue for paleoproterozoic oceans synchrotron source microprobe techniques xrf xanes and xrd and bulk geochemical analyses were used to examine the microscale distribution and speciation of mn fe and s as a function of depth in the top 48 cm of anoxic lake sediments manganese was primarily associated with calcite grains as a manganese rich carbonate that precipitated in the chemocline of the water column and settled through the euxinic basin to collect in lake sediments iron was preserved in framboidal iron sulfides that precipitated in euxinic bottom waters and underwent transformation to pyrite and marcasite in the sediments previous studies attribute the formation of manganese rich carbonates to the diagenetic alteration of manganese oxides deposited in basins underlying oxygenated water our study challenges this paradigm by providing evidence that mn bearing carbonates form in the water column and accumulate in sediments below anoxic waters consequently manganoan carbonates preserved in the rock record do not necessarily denote the presence of oxygenated bottom waters in ocean basins