geochemistry and nano mineralogy of feed coals mine overburden and coal derived fly ashes from assam north east india a multi faceted analytical approach abstract in order to address the scarcity of information on the nature and mode of occurrence of minerals and elements in coal coal mine overburden and coal ashes from north east india and also the relations between coal mineralogy and ash chemistry the petrology mineralogy and nano mineralogy and ash chemistry of some industrially important high sulfur coals mine overburden materials and fly ash samples from assam india have been evaluated a combined approach using petrography low temperature ashing plus x ray diffraction lta xrd field emission scanning electron microscopy fe sem high resolution transmission electron microscope hr tem raman spectroscopy and inductively coupled plasma mass spectrometry icp ms has provided new information on the mineralogy and nano mineralogy of these sub bituminous coals and associated mine overburden the presence of rare earth elements and yttrium rey in northeast indian coal mine overburden and fly ash samples is also reported for the first time the identification of these components may be significant from an economic point of view some northeast indian fly ashes with ree oxides up to 1580 ppm on an ash basis might possibly represent sources for recovery of rare earth elements

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

geochemical and paleomagnetic evidence for the occurrence of missing sapropels in eastern mediterranean sediments the cyclic occurrence of sapropels appears to be associated with maxima in the 65 n summer insolation target curve studies of the most recent sapropel have revealed extensive oxidation of organic matter or even the complete removal of this unit geochemical and magnetic signals allow for the detection of such a missing sapropel in older sediments these signals are altered by ongoing diagenetic processes an important parameter to reveal missing sapropels is ba elevated concentrations of ba are always found in visible sapropels and even after oxidation of part of the sapropel the initial ba profile remains visible we use this tool to trace down missing sapropels in kc01b a 37 m kullenberg core from the calabrian ridge eastern mediterranean at least 8 of 11 sampled intervals around insolation maxima contain evidence of a completely oxidized sapropel ba trace metal distributions and magnetic parameters are similar to those observed around visible sapropels

mineralogy of the pennsylvanian coal seam in the datanhao mine daqingshan coalfield inner mongolia china genetic implications for mineral matter in coal deposited in an intermontane basin abstract this paper deals with the mineral matter in the coal and associated strata from the datanhao mine daqingshan coalfield which is closely located to the previously reported adaohai and hailiushu mines of the same coalfield the coal from the datanhao mine is mainly high ash and low sulfur bituminous the mineral assemblage in the coal is dominated by quartz kaolinite with varying proportions of carbonates calcite ankerite and siderite small proportions of muscovite illite pyrite and anatase the associated non coal claystone samples have similar mineral assemblage except that most non coal samples contains less quartz than the adjacent coal plies although deposited in the same intermontane basin of the orogenic belt the yinshan upland the datanhao coal seam shows different mineralogical characteristics from those of the nearby adaohai and hailiushu mines this may reflect the different sediment source regions during the peat accumulation stage the sediment source for the datanhao coal was probably the ordovician quartz rich sandstone or the sinan quartzite in the surrounding sub uplifts high proportions of quartz in the datanhao coal suggest intense terrigenous input into the paleomire and a short distance from the sediment source region different mineralogical characteristics of the coals from the three mines datanhao hailiushu and adaohai of the daqingshan coalfield are probably due to the different source material in their respective surrounding subuplifts within the intermontane basin kaolinite displaying graupen tabular and vermicular textures and the common presence of quartz in the intra seam non coal bands from the datanhao coal seam indicate that most of these bands are tonsteins altered airborne volcanic ash the original magma is probably high level volatile rich silicic in composition

an appalachian isochron a kaolinized carboniferous air fall volcanic ash deposit tonstein the fire clay tonstein is a kaolinized airfall volcanic ash bed that was deposited in a widespread late carboniferous peat forming mire eleven samples from kentucky and west virginia spanning a distance of 200 km and two samples from tennessee and virginia indicate a characteristic mineralogical signature as compared with other appalachian tonsteins consisting of well crystallized kaolinite beta quartz crystal paramorphs sanidine ilmenite zircon and brookite detrital illite and quartz are rarely present or are in very small amounts which indicates rapid deposition in a mire several normal graded cycles in this tonstein suggest repeated episodes of pyroclastic activity that produced a composite ash layer a high silica alkalic rhyolitic source is suggested by the geochemistry of immobile elements and by electron probe analyses of glass inclusions in volcanic quartz from the fire clay tonstein the rare earth element plots chondrite normalized of the tonstein show a pronounced negative eu anomaly and relatively high concentrations of zr and th which are both indicative of a rhyolitic source probe analyses of the fire clay glass inclusions from four states indicate a chemically identical high silica rhyolite with peraluminous affinities 40 ar 39 ar sanidine plateau dating indicates an age of 312 1 ma for the fire clay tonstein which is consistent with previous 40 ar 39 ar dates for this tonstein this age is in agreement with a late westphalian b age in the european carboniferous chronostratigraphy on the basis of an age of 311 ma for the westphalian b c boundary a new isopachous map of the fire clay ash fall deposit indicates an area of 37 000 km 2 and a probable source to the present day southwest the deposit has a minimum preserved compacted volume of 2 8 km 3 which corresponds to an original uncompacted volume of about 20 km 3 this preserved volume indicates an ultraplinian volcanic explosion pindell and dewey 1982 proposed an andean type arc in this block during the late carboniferous prior to south american north american plate collision we hypothesize an associated back arc caldera system in the yucatan block to explain the high silica potassic rhyolitic ash that gave rise to the fire clay tonstein

mineralogy petrography and organic geochemistry of miocene coal seams in the kinik coalfield soma basin western turkey insights into depositional environment and palaeovegetation abstract the kinik coalfield is located in the south westernmost part of the soma basin in western turkey and hosts all three miocene coal seams from bottom to top km2 km3 and kp1 this study presents the coal petrographical mineralogical and organic geochemical features of samples collected from two deep cores samples from seam km2 generally display low ash yields and high toc content whereas the km3 and kp1 seams are characterized by relatively high ash yields and low toc values furthermore total s content of the kp1 is very high up to 7 0 on dry basis the maceral composition the coal facies diagrams and the distributions of n alkanes and diterpenoids indicate changes of depositional conditions and vegetation in the palaeomires of the km2 seam during early miocene the precursor peat of km2 seam started accumulating under limnotelmatic conditions followed by pure telmatic ones consequently initial mixed vegetation was replaced by a conifer dominant assemblage in the palaeomires in the upper parts of the km2 seam the coal facies indices and high concentrations of n alkanes along with the relatively low di di tri terpenoid ratios are indicators of the higher contribution of herbaceous species and minor abundance of conifers in the palaeomires of km3 and kp1 seams nevertheless the mineralogical composition of the km3 and kp1 seams indicate increased clastic input and alkalinity in the palaeomires that could reduce preservation of organic matter thus high ash yields and low toc were obtained from these seams in addition sulphate rich water supply along with synchronous pyroclastic air borne input into the palaeomires caused elevated total s content of the kp1 seam

diagenetic magnetic enhancement of sapropels from the eastern mediterranean sea diagenetic dissolution of magnetic minerals has been widely observed in organic rich sediments from many environments organic rich sediments from the eastern mediterranean sea sapropels recovered during leg 160 of the ocean drilling program reveal a surprising catalogue of magnetic properties sapropels from all sites studied across the eastern mediterranean sea are strongly magnetic and the magnetization is directly proportional to the organic carbon content the magnetization of the sapropels is dominated by a low coercivity probably single domain magnetic mineral with an inverse magnetic fabric that exhibits a clear decay in magnetic properties when exposed to air during heating the magnetic particles irreversibly break down between 360 and 400 c the contrast between the magnetic properties of sapropels and surrounding sediments is marked with remanence intensities of sapropels often being more than three orders of magnitude higher than those of underlying sediments the contrast between the magnetic properties of sapropels and the surrounding sediments is apparently controlled by non steady state diagenesis sulphate reducing conditions dominated during sapropel deposition while overlying sediments were deposited under oxic conditions the mineral responsible for the magnetic properties of sapropels is most likely to have formed under sulphate reducing conditions that existed during times of sapropel formation attempts to identify this mineral have been unsuccessful but several lines of evidence point toward an unknown ferrimagnetic iron sulphide phase the influence of diagenesis on the magnetic properties of cyclically deposited eastern mediterranean sedimentary sequences suggests that magnetic parameters may be a useful proxy for diagenesis in these sediments

the miocene coal seams in the soma basin w turkey insights from coal petrography mineralogy and geochemistry abstract the neogene soma basin western turkey hosts three coal seams km2 km3 and kp1 and several altered tuff layers within the miocene sequences this study focuses on the evaluation of coal petrography mineralogical and elemental compositions as well as the rock eval pyrolysis of the three coal seams from eynez isiklar and denis sectors and to identify the mineralogy of altered tuff layers within km2 and kp1 seams the routine coal quality analyses show that coal samples from the km2 seam are characterized by lower ash yields and total s contents and higher gross calorific values than km3 and kp1 seams the mineralogical composition of the bulk coal samples varies between all three seams the statistical treatment implies that major elements in bulk coal samples such as al fe k mg and na and the vast majority of minor and trace elements have inorganic affinity the trace element contents and elemental enrichments in the coal samples are generally changeable from seam to seam which could be related to differences in ash yield and mineralogy altered tuff layers or tonsteins were identified in km2 and kp1 seams the tonsteins are clay rich and certain trace elements e g as and zr are enriched in the coal layers beneath the tuff layers in the km2 seam this might be related to penetration of leached pore water into these layers and precipitation of epigenetic minerals the coal petrography composition and the coal facies diagrams show that the precursor peat of the km2 seam was accumulating under telmatic mesotrophic anoxic conditions whereas the water level was high and stable the relatively low ash yields and thicker coal beds suggest a lower clastic input from the basin margins and water table fluctuations resulted in calcareous intercalations in the km3 and kp1 seams these imply the development of limno telmatic conditions whereas fluvial activity affected during peat accumulation of both seams considering the maceral composition along with the coal thickness coal seams in the soma basin might display oil generation potential however the pyrolysis analysis shows that the studied coal seams are mainly gas prone and only certain coal beds have mixed hydrocarbon generation capacity all data presented in this study indicates that lithological features differences in coal qualities and elemental contents in the soma basin were mainly controlled by changes in the depositional conditions and the detrital input during miocene

magnetic measurements used to identify paleoxidation fronts in deep sea sediments from the madeira abyssal plain we describe the results of rock magnetic measurements of a sediment core from the madeira abyssal plain which contains multiple turbidites previous studies of trace element e g u concentration and observations of sediment color changes have shown that turbidite emplacement has resulted in reductive diagenesis and the formation of paleoxidation fronts we show that variations in sediment lithology and postdepositional sedimentary processes can be characterized very sensitively using magnetic measurements low concentrations of magnetic minerals occur in turbidites with a high organic content reflecting the destruction of magnetic material via the process of reductive diagenesis in addition fossil redox fronts are readily identified by rock magnetic properties

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

diagenesis in anoxic sediments from the california continental borderland and its influence on iron sulfur and magnetite behavior solid phase and pore water profiles of compounds containing iron and sulfur have been determined by wet chemical magnetic and x ray diffraction techniques in three california continental borderland basins the observed profiles have been fit by simple reaction diffusion models in order to determine reaction rates and constrain budgets for iron and sulfur more than 95 of the solid phase reduced sulfur is pyrite and down core profiles are well fit by a model in which net sulfate reduction rates decrease exponentially with depth net sulfate reduction rates determined from models fit to solid phase reduced sulfur measurements and pore water sulfate profiles yield results that are consistent depth integrated sulfate reduction rates for modern sediments in san pedro santa catalina and san nicolas basins are 11 4 6 3 and 6 3 8 8 mol cm 2yr 1 respectively measurements of solid phase iron species indicate that surficial sediments are enriched in easily reducible ferric oxyhydroxides the enrichment is maintained by a combination of oxidation of fe2 diffusing upward from underlying anoxic sediments as well as input of fresh sediment enriched in ferric oxyhydroxides the three primary sources for iron converted to pyrite and the sequence in which they are utilized are ferric oxyhydroxides magnetite and other crystalline oxides and exchangeable iron in phyllosilicates the majority 50 80 of the iron converted to pyrite is from the silicates and budgetary calculations indicate the amount of iron released from san pedro basin silicates agrees within 35 with the amount of magnesium removed from pore water to solid phases fe2 is enriched in near surface pore waters because rates of dissolved iron production by oxyhydroxide reduction exceed rates of sulfate reduction and pyrite formation at depth pore waters are sulfidic because rates of sulfate reduction exceed rates of iron release from silicates sulfide produced at depth diffuses upward until it reaches sediments with available iron causing a step like increase in solid phase sulfur concentration over 90 of the magnetite present in surficial sediments is dissolved at depth due to reaction with h2s a model is developed to predict the depth at which magnetite dissolution should occur based on sulfate reduction rates and the flux of ferric oxyhydroxides the results of this model predict the onset of dissolution at depths of 5 40 cm in different basins and agree well with the observed depths of magnetite dissolution

coal rank and petrography of upper carboniferous seams in the amasra coalfield turkey abstract the amasra coalfield is a part of the upper carboniferous zonguldak coal basin of turkey within the istanbul zone a hercynian deformed unit forming the eastern continuation of the moesian platform in se europe which was later deformed by alpine tectogenesis the mainly westphalian aged coals were sampled from an underground mine and from cores from nine exploration wells and petrographic maceral and microlithotype analysis and mean maximum vitrinite telocollinite reflectance r max in oil were determined the coals were characterised by low ash and low total sulphur contents abundant vitrinite group macerals and relatively abundant vitrite clarite and duroclarite microlithotypes vitrinite reflectance was in the range 0 58 1 04 r max indicating ranks from high volatile c bituminous to high volatile a bituminous coal the r max generally increases with increasing depth in the exploration wells with gradients ranging from 0 21 to 0 40 r max km and an average of 0 30 r max km the highest value occurs in the south of the coalfield in a region of hercynian folding and thrusting the relationship between vitrinite reflectance and thrusts in the wells suggests that coal rank was developed mainly pre thrusting but that some wells arguably show evidence for post thrust coalification peak coalification probably occurred during late mesozoic early tertiary rifting so that the thrusts which developed after coalification are likely to be alpine in age whereas the thrusts that pre date coalification may have been hercynian structures

controlled biomineralization of magnetic minerals by magnetotactic bacteria magnetotactic bacteria produce two general types of minerals as the mineral phases of their magnetosomes iron oxides and iron sulfides the iron oxides include only ferrimagnetic magnetite fe3o4 and the iron sulfides ferrimagnetic greigite fe3s4 and non magnetic pyrite fes2 regardless of composition the magnetosome particles have a very narrow size range 35 120 nm and are single magnetic domains these intracellular particles confer a permanent magnetic dipole moment to the cell resulting in the cell s magnetotactic response i e a motile biomagnetic compass the morphology of the magnetosome particles is species and or strain specific thus the organism exerts significant control over the biomineralization process es involved in magnetosome formation however there is some accumulating evidence that suggests that in certain organisms under specific situations local environmental conditions appear to affect the magnetosome mineral phase in at least three different ways these include 1 variations in the stoichiometry of the metal and non metal components of the magnetosome mineral phase 2 the replacement of iron with other transition metal ions in the metal component of the magnetosome mineral phase and 3 the replacement of oxygen with sulfur or vice versa in the non metal component of the magnetosome mineral phase examples of each type of mineral change or variation are described and discussed

non steady state magnetic mineral reduction chemical lock in and delayed remanence acquisition in pelagic sediments abstract magnetic hysteresis data collected from pelagic sediment sites in the western equatorial pacific ocean define a progressive deepening of modern redox boundaries with decreased organic carbon input paleomagnetic data from the site with the highest organic carbon shows marked changes in the natural remanent magnetization at the modern fe redox boundary suggesting a type of chemical lock in process in which some magnetic grains form in situ above the boundary and freely orient in the field the depth of chemical lock in suggests paleomagnetic data will be smoothed on time scales ranging from less than 40 kyr to more than 425 kyr the higher values are compatible with models calling for a delayed remanence acquisition to account for the saw tooth pattern observed in some sedimentary paleointensity records

magnetite diagenesis in marine sediments from the oregon continental margin the magnetochemistry of sediments from the oregon continental margin is examined to determine the effects of iron sulfur diagenesis on the paleomagnetic record magnetic mineral dissolution and transformation into iron sulfides are a common feature in these suboxic to anoxic lutites these processes are evidenced in rapid decreases in natural remanent magnetization intensities and stabilities systematic changes in other rock magnetic properties and increases in solid phase sulfur concentrations with depth hysteresis measurements are used to evaluate downcore changes in magnetite concentration and grain size magnetite abundances decrease downcore from initial values of about 0 1 and nominal grain diameters lie within a narrow pseudosingle domain range of 0 08 to 0 6 m a first order surface area reaction model da dt ka is proposed to explain the magnetite dissolution mechanism where a is the total magnetite surface area and k is the rate constant the solution of this equation predicts that the surface area and concentration decrease exponentially and the concentration in addition depends on grain size application of this model in two cores where grain size varies with depth successfully explains the downcore profiles of both concentration and surface area despite extensive magnetite destruction magnetic directions in such sediments appear to reliably record long wavelength trends of the geomagnetic field

the late diagenetic conversion of pyrite to magnetite by organically complexed ferric iron abstract the geochemistry of late stage diagenetic replacement of pyrite by magnetite was investigated by laboratory experiments of pyrite dissolution and magnetite precipitation involving organically complexed ferric iron the design of the experiments is based on the hypothesized geochemical conditions for in situ diagenesis in the pennsylvanian age belden formation an organic rich carbonate in northwestern colorado with pyrite grains rimmed with magnetite that contains a cretaceous paleopole position the geochemistry is applicable to both deep and near surface reactions involving pyrite magnetite and organic matter and bears upon the geologic interpretation of secondary chemical remanent magnetizations crm aqueous solutions of ferric ligand complexes and pyrite were heated 60 c for 60 days in the absence of light and at low partial pressures of oxygen additional experiments with each ligand were performed both in the presence of bentonite and without ferric iron ligand only raising the ph to 8 5 produced a ferrous hydroxide precipitate and subsequent heating 90 c resulted in the formation of magnetite ferric complexes of oxalate salicylate and acetylacetonate resulted in pyrite dissolution and magnetite formation the activity of strongly reducing ligands e g catechol or unsaturated fe iii exchange capacity particularly in experiments with bentonite or with solutions of uncomplexed ligands can result in an effective reduction of ferric iron concentration and prevent pyrite dissolution and or interfere with the crystallization of magnetite the bentonite acted to adsorb dissolved species and also underwent direct dissolution especially by the oxalate ligands although these reactions could occur at any depth a continuing supply of molecular oxygen more available in near surface settings would result in the formation of hematite or the production of acidic sulfate conditions whereas at greater depths or restricted porosity the redox gradation is halted at magnetite the results of this study thus provide a likely geochemical mechanism for the replacement of pyrite by magnetite during the latter stages of diagenesis

early sediment diagenesis on the blake bahama outer ridge north atlantic ocean and its effects on sediment magnetism sediment magnetic and geochemical studies of a suite of deep sea sediment cores from the blake bahama outer ridge bbor north atlantic ocean have identified two current redox boundaries in surficial holocene carbonate rich sediments over much of the bbor the upper mn 4 mn 2 redox boundary is associated with a spike in the concentration of solid phase mn as mno2 the lower fe 3 fe 2 redox boundary is associated with a spike in the concentration of solid phase fe as goethite feooh over much of the bbor high sediment magnetic intensities occur in surficial carbonate rich sediments associated with these redox boundaries and lower intensities occur in deeper late pleistocene carbonate poor sediments this relationship is opposite to that expected if sediment magnetism simply reflects the clastic noncarbonate sediment fraction the surficial high sediment magnetic intensities are due primarily to the following two factors 1 magnetic mineral authigenesis associated with early diagenesis and 2 the presence of abundant 0 1 m magnetite crystals interpreted to be bacterial magnetosomes magnetosomes are almost absent in the late pleistocene low carbonate sediments owing most likely to local pleistocene environmental conditions high clastic flux low organic flux which did not favor their growth the sediment natural remanent magnetization is strongly correlated with the sediment clastic fraction and is relatively unaffected by early diagenesis and the presence of abundant bacterial magnetite if this is typical bacterial magnetite may be more abundant in nature but less important to sediment paleomagnetic records than previously thought

occurrence and genesis of tonsteins in the miocene lignite tuncbilek basin kutahya western turkey abstract abundant beige and white kaolinite claystone layers 2 50 cm thick from the tuncbilek basin have the characteristics of tonsteins the aim of this study was to determine the mode of formation of the tonsteins together with their mineralogical and geochemical characteristics in order to identify their environment of deposition the miocene lacustrine units in the tuncbilek lignite deposit associated with tuff and tuffite are comprised of organic rich shale organic rich marl marl claystone silty claystone siltstone sandstone coal seam and conglomerate deposited in a fluvial and lacustrine environment sanidine plagioclase biotite and chlorite are partly to completely argillized and enclosed in an authigenic clay matrix in the rhyolitic to rhyodacitic tuff tuffite sandstone organic rich shale and serpentinite host rocks of the clay deposit abundant kaolinite and quartz are associated with smectite illite feldspar calcite dolomite siderite pyrite barite and gypsum development of oriented 7 a halloysite tubes on in altered volcanogenic materials associated with kaolinite and the occurrence of vermiform kaolinite edging disordered kaolinite locally siderite and pyrite crystals may suggest formation of halloysite following kaolinite the reaction pathway is volcanic glass feldspar muscovite biotite 7 a halloysite kaolinite the slight enrichment of light rare earth elements lree compared to heavy rare earth elements hree with positive eu anomalies based on upper continental crust ucc normalized values reflects fractional crystallization of feldspar and amphibole in the parent volcanic rocks and organic rich shale alteration of feldspar biotite and volcanic glass resulted in the concentration of al si fe mg and k and precipitation of kaolinite in an acidic open hydrological system while in a stagnant and alkaline environment smectite and illite are the alteration products the al2o3 tio2 and low cr ni ratios suggest felsic parent rocks the trace elements ratios such as ni co v cr cu zn and u th among the basement complex source rocks units also suggest oxic suboxic and anoxic conditions the occurrence of pinus alnus quercus alnus carya taxodiaceae and myrica palymorphs reflect a subtropical to warm temperature humid climate low elevations and swamp vegetation condition during the early middle miocene period in the study area association of argillization and silicification with coal pyrite and gypsum indicates a swampy environment and hydrothermal processes this interpretation is corroborated by the calculated formation temperatures from stable isotope analysis of 148 8 168 c for kaolinite and 145 169 2 c for smectite the low s isotope values of pyrite 19 to 2 9 and high positive values of gypsum 11 5 21 7 indicate a mixed diagenetic and hydrothermal origin for the sulfide and sulfate mineral

the geology mineralogy petrography and geochemistry of the miocene dursunbey coal within fluvio lacustrine deposits balikesir western turkey abstract the dursunbey coalfield a typical example of coalfields in the western anatolia hosts a mineable coal seam about 9 0 m coal thickness with altered tuff layers within early miocene fluvio lacustrine sequences the aim of this study is to identify peat accumulation conditions and factors controlling the mineralogy and geochemistry of this seam the standard coal features and petrographical mineralogical and elemental compositions display changes throughout the seam ash yields display decreasing trends towards to the upper parts of seam while total c contents and gross calorific values are increasing furthermore the coal facies patterns evidence changes of depositional conditions and vegetation in the palaeomires during initial stages of peat accumulation the contribution of herbaceous peat forming plants were more common and palaeomires were open to detrital inputs whereas woody peat forming were becoming predominant and the water table was stable and high which caused development of anoxic conditions during late stages therefore the content of detrital minerals such as quartz and clay minerals illite smectite and chlorite increases in the lower parts of seam while that of pyrite increases in the upper parts in addition the sem edx data show that matrices of clay mineral aggregates are illitic in composition in the lower parts of seam while those of smectite prevalence are more common below and above altered tuff layers interestingly authigenic rhomboid k feldspar grains are observed within smectite clay aggregates in the samples from the upper parts of seam framboidal pyrite grains and clusters were also commonly identified from these samples as well this data shows that synchronous volcanic inputs were altered within a hydrologically closed system under slight acidic to neutral conditions during late syngenetic stages the enriched elements such as cr ni cs and v display moderate to strong positive correlations with ash yields while al2o3 and k2o indicate an aluminosilicate affinity clay mineral and feldspar considering the presence of metamorphic and ophiolitic rocks in the basement and the adjacent areas clastic inputs into the palaeomire seems to be controlling aluminosilicate affiliated elements additionally the sem edx analyses denoted that ni and as are associated with pyrite the ni and as bearing epigenetic pyrite infillings are mostly identified in coal samples below altered tuff layers hence as and ni enrichments are controlled by precipitation of leached pore waters from altered tuff layers nevertheless as and ni bearing syngenetic pyrite grains and clusters are related with the development of anoxic conditions within palaeomires this could also favour a mo and u enrichment which is another testimony for synchronous volcanic inputs altered under anoxic conditions overall high detrital input ratios from adjacent areas during initial stages of peat accumulation in the study area controlled by enrichments of aluminosilicate affiliated elements whereas during late stages of peat accumulation the development of a hydrologically closed system and redox conditions within the palaeomire caused as ni mo and u enrichments and the formation of smectite and authigenic k feldspars

bituminous coal seams from underground mines in the zonguldak basin nw turkey insights from mineralogy coal petrography rock eval pyrolysis and meso and microporosity abstract the zonguldak basin contains the main bituminous coal reserves of turkey ca 1 4 gt and several coal seams are mined in underground coal mines within the basin this study focuses on coal petrography mineralogy rock eval pyrolysis and the meso and microporosity characteristics of the coal samples collected from several late carboniferous pennsylvanian bituminous coal seams in the basin forty channel samples were collected from various coal seams in underground mines at the armutcuk zonguldak and amasra coalfields in the zonguldak basin the studied coal samples have low total moisture contents avg 2 3 on as received basis low total s contents avg 0 5 on dry basis and relatively high ash yields avg 21 2 on dry basis the random vitrinite reflectance values 0 69 1 21 and gross calorific values avg 33 0 mj kg on dry ash free basis indicate that the coal samples are of high volatile c bituminous to medium volatile bituminous coal minerals identified by xrd in bulk coal samples are clay minerals mainly kaolinite and rarely illite and chlorite quartz and carbonates calcite dolomite and siderite in a few samples pyrite and feldspar were also identified the sem edx analyses performed on the carbon coated polished blocks imply that the carbonate minerals are mainly epigenetic whereas the silicate minerals are generally syngenetic in origin the results of low pressure n2 adsorption analysis indicate that the bet surface areas 1 1 5 5 m2 g and mesopore volumes 0 003 0 011 cm3 g vary within a wide range the results of the low pressure co2 adsorption analyses show that micropores are abundant in the coal samples however the bet surface areas 10 41 78 11 m2 g and micropore volumes 0 010 0 049 cm3 g vary widely among the three coal mines and different coal seams our results suggest that variations in the mesopore characteristics are mainly controlled by mineral matter while microporosity is controlled by a combination of organic matter maceral compositions and coal rank of the studied coal seams

sedimentology and stratigraphy of the amasra coalfield pennsylvanian nw turkey new insight from a 1 km thick section abstract we report on a sedimentological and biostratigraphic evaluation that was carried out on an approximately 1 km thick coal bearing pennsylvanian succession encountered in the boreholes hema 82 and 85 in the amasra coalfield of the zonguldak amasra coal basin turkey results of the study include a refined interpretation of sedimentary environments of the coal bearing strata and their cyclic patterns improved constraints on macrofloral biozones as well as of boundaries and thickness of lithostratigraphic units a paleosol based climatic trend is also proposed and the tectono sedimentary history of the amasra coalfield is compared with other coal basins in europe stratigraphically constrained macroflora confirms a recently suggested discontinuous sedimentary record that contrasts with the previously widely accepted opinion that deposition was continuous throughout the pennsylvanian hiatuses were identified between each adjacent formation an early asturian hiatus between the karadon and kizilli formations has its equivalent in other variscan basins of europe namely in the dobrudzha upper silesian intra sudetic and central and western bohemian basins it is in agreement with the former paleogeographic position of the zonguldak amasra basin and its basement in the southern margin of laurussia in the eastern continuation of these central european basins this conclusion is further supported by paleosol morphology based climatic trend to increasing aridity around the westphalian stephanian boundary observed in the studied boreholes and identical with a similar trend in the above mentioned central european basins

coal petrography mineralogy elemental compositions and palaeoenvironmental interpretation of late carboniferous coal seams in three wells from the kozlu coalfield zonguldak basin nw turkey abstract a number of coal seams of late carboniferous age in the coal bearing karadon kozlu and alacaagzi formations have been mined in several deep underground mines in the zonguldak basin nw turkey for this study a total of 154 coal core samples were collected from three research wells that were drilled in the tectonically complex settings of the kozlu coalfield all the coal samples were studied by means of coal petrography mineralogy and geochemistry special attention was given to the compositions and origins of fracture cleat filling minerals that were identified by sem edx on polished blocks the coal seams investigated are of bituminous rank they are characterized by low total sulphur contents 1 0 on dry basis and high gross calorific values 22 5 40 2 mj kg on dry ash free basis whereas ash yields and volatile matter contents are variable x ray powder diffraction data indicate that the mineralogical compositions of the studied coal seams are rather similar and clay minerals along with quartz and carbonate minerals were identified in almost all seams the statistical evaluations and sem data show that some elements such as mg ti zr nb and th are generally affiliated with silicate minerals whereas elements like cu zn mo and pb are mainly associated with sulphide minerals the silicate minerals are generally detrital and the majority of carbonate minerals are of epigenetic origin the epigenetic carbonate and sulphide minerals suggest that circulated solutions within coal seams were mainly derived from ca2 rich solutions leached from overlying formations such as cretaceous aged zonguldak formations and from hydrothermal solutions that likely were derived from andesitic dykes within the basin the regional tectonic activities during coalification seem to have deformed coal bearing formations and therefore intra basinal solutions could have penetrated into the studied coal seams the epigenetic mineralisation also resulted in elemental enrichments and elevated ash yields total sulphur and volatile matter contents in some coal seams thus deformation during coalification controlled some coal quality parameters in the studied wells the coal facies diagrams suggest that palaeomires mostly accumulated under limno telmatic conditions whereas a telmatic environment was more common in palaeomires of the kozlu formation coal petrography suggests that peat forming vegetation and water tables in palaeomires were changeable during the late carboniferous

late holocene erosion in nw anatolia from sediments of lake manyas lake ulubat and the southern shelf of the marmara sea turkey abstract this paper deals with modern and ancient sedimentation in fresh water lakes and the marine shelf of the southern marmara region nw anatolia turkey most of the information has been obtained from monitoring of suspended load discharged into two lakes manyas and ulubat in the last 45 years and from 8 to 11 m thick lacustrine sediments in addition to radiocarbon dated shelf sediments this allows a holistic approach to the drainage basin denudation over time the results show that the sedimentation rates in the lakes were low 0 22 cm year 1 from 4000 to 2000 years bp and then they increased 0 29 cm year 1 up to sub recent times and reached 0 44 cm year 1 in the last century it is suggested that deforestation created high rates of sedimentation in the basins and or strong denudation of the region during the late holocene this study also shows that for shallow freshwater lakes the calculation of sedimentation rates must include fine particles lost by the outlets and coarse grained bed load deposited on their shores in addition a high rate of sedimentation has been created by short but repetitive intense depositions during the last century particularly during the last 45 years the rate of sedimentation or denudation has increased dramatically in nw turkey the two world wars and mismanagement of the land had important local effects by increasing deforestation and resulting in the present erosive conditions

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

the holocene climatic optimum and pollen records of sapropel 1 in the eastern mediterranean 9000 6000 bp abstract the most recent sapropel in the deep eastern mediterranean sea has been deposited between 9 and 6 ka bp climate conditions as revealed by the pollen records of this sapropel in marine cores were most favorable for temperate deciduous trees which is in agreement with the inferences from records of peripheral land pollen sites the abundance of deciduous oak pollen is much higher than that of artemisia sage brush indicating that annual precipitation in the mid elevation borderlands was at least 550 mm without summer drought but more probably in the range 800 1300 mm the pollen of pistacia which formed a savanna at low elevations is also at its highest abundance and signals the absence of frost in winter while being capable of withstanding summer drought the early holocene therefore appears as the post glacial climatic optimum with the highest moisture and mildest winters in southwest asia this is also the time of the neolithic population explosion with incipient domestication of cereals possibly following natural selection of the tough rachis mutation in wheat and barley by the extreme aridity of the preceding younger dryas

pyroclastic kaolin coal tonsteins of the upper carboniferous of zonguldak and amasra turkey abstract the existence of pyroclastic kaolin coal tonsteins tonsteins smectites from upper carboniferous strata of the coal mining region of zonguldak and amasra north western turkey is reported in the area of zonguldak tonsteins were discovered within the seams pic ii and piric asma 5 mine of the kozlu formation westphalian a in the area of amasra tonsteins occur in the seams kalin and tavan tarlaagzi mine of the karadon formation westphalian b c thin sections were prepared to investigate mineral composition and texture detailed descriptions are presented kaolinite is the predominant mineral in the tavan tonstein montmorillonite illite is also present pyrogenic phenocrysts prove that the tonsteins are alteration products of volcanic ashes therefore a wide lateral distribution of these layers can be expected these tonsteins represent very suitable stratigraphic markers in the upper carboniferous strata of northwestern turkey

elements and phosphorus minerals in the middle jurassic inertinite rich coals of the muli coalfield on the tibetan plateau abstract the content modes of occurrence and origin of elements and phosphorus minerals in the jurassic coals of the muli coalfield on the tibetan plateau were investigated using optical microscopy field emission scanning electron microscopy in conjunction with energy dispersive x ray spectrometry x ray powder diffraction x ray fluorescence spectrometry and inductively coupled plasma mass spectrometry the muli coals l1 and l2 coals are of high volatile a bituminous to medium volatile bituminous rank characterized by low sulfur contents and are generally dominated by the inertinite group macerals predominantly semifusinite and fusinite the l1 coal contains abundant apatite 7 9 on average on an organic matter free basis and alumino phosphate minerals of goyazite gorceixite crandallite group 4 9 on average and accordingly the concentrations of elements f 253 g g on average p 2349 g g sr 526 g g and ba 790 g g are elevated as compared with common world hard coals the deposition of phosphorous bearing minerals in the muli coals was not derived from volcanic input penetration of ca and al rich solutions release of phosphorus from organic matter during plant decay and an appropriate sedimentary environment such as low ph low water table for peat and oxidizing conditions were critical factors in deposition of the phosphorus minerals

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the eastern mediterranean sea summary magnetic properties irm arm xin s ratio at 0 3 t room temperature rt hysteresis and thermomagnetic curves and geochemical data fe s mn al ti organic c were studied in two eastern mediterranean boxcores abc26 and bc19 at a resolution of 3 5 mm the boxcores contain sapropel s1 9 6 kyr bp at a few decimetres below seafloor the magnetic fraction consists predominantly of single domain sd to pseudo singledomain psd magnetite in the entire cores the original input of magnetic grains comes from two sources aeolian dust both cores and volcanic ash from the minoan eruption of santorini core bc19 only non steady state diagenesis has changed the magnetic mineralogy considerably in these alternating organic rich organic poor sediments during deposition of sapropel s1 reductive diagenesis and pyritization in and just below the sapropel caused lower magnetic intensities coarser magnetic grain sizes and partial maghemitization in thermomagnetic curves two types of pyrite can be identified one oxidizes below 450 uc and the other above 450 uc the higher oxidation temperature is predominantly found below the sapropel this may be related to the microtexture of pyrite which is euhedral below sapropels and mainly framboidal within sapropels since the end of sapropel deposition a downward moving oxidation front has oxidized the upper half c 5 cm of the sapropel the oxidized part of the sapropel is enriched in diagenetically formed fe oxides with relatively high coercivity and arm the maximum coercivity is found in a distinct layer between the present day mn and fe redox boundaries at the top of the unoxidized sapropel the freshly precipitated fe oxides in this centimetre thick layer contain a mixture of superparamagnetic sp grains and high coercivity sd magnetite higher in the oxidized zone the freshly precipitated fe oxides have aged into generally slightly lower coercivity sd grains with relatively high arm in addition to the diagenetic formation of fe oxides at the top of the sapropel formation of a ferrimagnetic fe monosulphide may have occurred within the sapropel during later stages of diagenesis which may have enhanced the arm signal in the organic rich interval in particular

high precision 40ar 39ar spectrum dating on sanidine from the donets basin ukraine evidence for correlation problems in the upper carboniferous two 40 ar 39 ar spectrum measurements on well preserved volcanic feldspar sanidine from the coal tonstein horizon 1 3 1 from the lower kashirsky group middle moscovian stage of the donets basin upper carboniferous ukraine yielded well defined plateaus with an average age of 305 5 1 5 ma the age is to be interpreted as sedimentation age of the coal tonstein and thus defines a chronostratigraphic time mark in the east european carboniferous taking the correlation of the 1 3 1 horizon and the recently published time scales for the upper carboniferous as a basis for comparison the age of 305 5 ma is about 6 ma too young this age discrepancy obviously points to inaccurate or even erroneous correlation and we therefore are compelled to suggest a reconsideration of the validity of the current biostratigraphic correlation between the carboniferous of western and east europe

cyclic variations in the chemical composition of eastern mediterranean pliocene sediments a key for understanding sapropel formation abstract two pliocene mediterranean sediment cores from ocean drilling program odp leg 160 sites 964 pisano plateau ionian basin and 967 lower northern slope of eratosthenes seamount south of cyprus have been analyzed for major and minor elements si ti al fe mg ca k ba cr ni v zn zr by x ray fluorescence analysis at a depth resolution of 3 to 4 cm a total of 430 samples core 964c 9h comprises five sapropels with up to 9 7 total organic carbon toc one 2 5 m thick turbidite and a 50 cm segment of a second turbidite whereas core 967b 9h contains eight sapropels with toc contents of up to 6 7 cyclic variations in carbonate content and detrital matter composition are evident at both sites at site 964 pisano plateau terrigenous detrital matter chemistry reflects periods of stronger saharan dust input higher si al and zr al ratios alternating with fluvial input from the northern borderlands higher mg al ratios cyclicity is not well expressed at this location because turbidites and winnowing occur site 967 eratosthenes seamount sediments are strongly influenced by discharge from the nile river during humid periods low k al and mg al ratios at site 967 sapropels occur only during periods of enhanced nile discharge with correspondingly lower si al ti al mg al k al and zr al ratios accumulation rates of carbonate and terrigenous detrital matter were 30 lower during such episodes because of the reduction in eolian input and carbonate production and or carbonate dissolution periodical ba enrichments which are not only seen in the sapropels but in every k al minimum document the association of enhanced bioproductivity and sapropel formation as calculated from excess ba concentrations productivity increased by up to a factor of five during intervals of intensified nile runoff fluviatile discharge seems to be responsible for an enhanced input of nutrients and suspended matter containing low mg al and k al ratios based on organic carbon concentrations episodes of sapropel formation lasted at least from 1000 to 4000 years at site 964 and from 2000 to 6000 years at site 967 periods of enhanced bio productivity as defined by ba enrichments lasted from 8000 to 12 000 years at site 967 episodes of high river discharge and corresponding nutrient input as well as conditions of sapropel formation seem to have lasted longer in the eastern part of the basin site 967 than at the pisano plateau site 964

rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the california continental borderland the rock magnetic properties of marine sediments from the california continental borderland san pedro santa catalina and san nicolas basins have been studied in order to quantitatively assess the effects of sediment diagenesis on magnetic minerals previous studies have noted that the natural remanent magnetization in these sediments primarily carried by detrital magnetite decays to 10 or less of its surface value soon after deposition this decrease is caused by magnetite dissolution related to sediment diagenesis and is unrelated to paleoclimatic variations or changes in the regional influx of detrital magnetic material detailed rock magnetic measurements show that shifts to softer remanent coercivity and differences in the rate and degree of magnetic intensity loss with depth can be related to the dissolution process the shift to softer remanent coercivity is related to a coarsening of the magnetic mineral grain sizes with depth due to preferential dissolution of the finest grained magnetic material the intensity decreases which are linearly proportional to magnetite concentration decreases indicate that dissolution occurs with rate constants ranging from 0 3 to 1 6 kyr 1 the rate constants sulfide concentrations and magnetite grain size estimates from the borderland are consistant with previous studies of magnetite dissolution our results demonstrate the importance of both sulfide and magnetite surface area in the dissolution process anomalous peaks in viscous remanence within the sediments suggest the authigenic growth of greigite and its subsequent transformation to pyrite

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

mineralogy of the volcanic influenced great northern coal seam in the sydney basin australia abstract the mineralogy of the individual coal plies and intra seam claystone bands in the great northern seam of the sydney basin has been evaluated using optical and scanning electron microscopy and quantitative x ray diffraction techniques the uppermost two claystone bands are tonsteins consisting mainly of well ordered kaolinite with graupen to vermicular textures idiomorphic crystals of k feldspar within these tonsteins may represent members of the anorthoclase sanidine series or a sodic sanidine and indicate an acid to intermediate volcanic ash input in contrast the lowermost parting was largely derived from epiclastic sediment admixed with minor volcanic material such as high temperature quartz and a different type of k feldspar component the mineral fraction of the coals especially in the middle and upper parts of the seam is dominated by authigenic kaolinite with a very low abundance of quartz apart from the tonsteins authigenic processes therefore appear to be the dominant mechanism of mineral matter formation authigenic k feldspar also occurs in the lower few metres of the seam with a variety of modes of occurrence including cell and cleat infillings cross cutting veins and thin laminae parallel to the organic matter and detrital clay bands a late syngenetic low temperature hydrothermal fluid injection process is suggested for formation of the feldspar veins the origin of the fluid is uncertain but is most likely associated with contemporaneous volcanic activity

magnetic mineral diagenesis in suboxic sediments at bettis site w n ne pacific ocean the effects of iron diagenesis on paleomagnetism and rock magnetism were examined in suboxic sediments from bettis site w n in the ne pacific ocean as part of the oxidative decomposition of organic matter ultrafine grained authigenic magnetites are produced immediately above the iron reduction zone this zone is commonly observed in deep sea sediments as a prominent color change from brown to greenish grey the magnetite authigenesis is evidenced by systematic increases in natural magnetic intensities and stabilities and by comparable shifts in other rock magnetic properties the magnetites are composed of relatively pure fe3o4 and fall within a restricted size range of 0 06 0 12 m which is nominally single domain some of these finest grained magnetites are rapidly destroyed during burial upon entering the zone of iron reduction leaving a relatively coarser population magnetite dissolution appears to continue with depth according to a first order surface area reaction process when at steady state iron reduction is independent of sulfide formation in these sediments because solid sulfur profiles show no increase at depth and most of the sulfur occurs as barite despite a well constrained carbonate stratigraphy comparisons of paleomagnetic directions between nearby cores show little agreement suggesting that the directions are composed of a complex mixture of remanences acquired at different depths subsurface magnetic peaks may represent paleoredox markers preserved by non steady state redox conditions caused by climatically induced variations in organic matter flux and sedimentation rates

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels