magnetic properties of hydrothermally synthesized greigite fe3s4 i rock magnetic parameters at room temperature summary greigite of variable purity has been synthesized hydrothermally at 140 c by injecting a mohr s salt solution into a sodium sulphide solution containing dissolved zerovalent sulphur ageing for 30 960 min and rapidly quenching oxygen was rigorously excluded during the synthesis scanning electron microscope sem observations yield a grainsize range up to 400nm the variable purity was deduced from a varying specific saturation magnetization 3 29 am2 kg i the mjm or ors os ratio varies between 0 3 and 0 4 which is indicative of fine grained greigite concurring with sem observations hysteresis measurements at low temperatures indicate the presence of grains that are superparamagnetic at room temperature coercivity parameters b 13 43 mt bo cr 37 73 mt are the highest obtained to date for synthetic greigite and compare well with those measured for natural greigite ranges for other rock magnetic parameters are discussed greigite hysteresis parameters overlap those of magnetite to a large degree a diagnostic interparametric ratio for greigite is its high o xin ratio the range of the present greigite is 40 75 kam

magnetic properties of sedimentary greigite fe3s4 an update greigite fe3s4 is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction it can also grow at any time when dissolved iron and sulfide are available during diagenesis greigite is important in paleomagnetic environmental biological biogeochemical tectonic and industrial processes much recent progress has been made in understanding its magnetic properties greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites the crystallographic c axis is the easy axis of magnetization with magnetic properties dominated by magnetocrystalline anisotropy robust empirical estimates of the saturation magnetization anisotropy constant and exchange constant for greigite have been obtained recently for the first time and the first robust estimate of the low field magnetic susceptibility is reported here the curie temperature of greigite remains unknown but must exceed 350 c greigite lacks a low temperature magnetic transition on the basis of preliminary micromagnetic modeling the size range for stable single domain behavior is 17 200 nm for cubic crystals and 17 500 nm for octahedral crystals gradual variation in magnetic properties is observed through the pseudo single domain size range we systematically document the known magnetic properties of greigite at high ambient and low temperatures and with alternating and direct fields and illustrate how grain size variations affect magnetic properties recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records including widespread remagnetizations

chronostratigraphy of sediment cores from the bering sea and the subarctic pacific based on paleomagnetic and oxygen isotopic analyses the chronostratigraphy of six piston cores collected from the bering sea and one piston core from the subarctic pacific is reported age models are primarily based on oxygen isotope data from cores bow 8a and es in conjuction with relative paleointensity proxy records biogenic opal data and a radiolarian datum from other cores whose sediments mainly consist of diatom microfossils and poorly preserved calcium carbonate the records the first paleointensity proxy reported from the bering sea show that characteristic paleointensity lows at 40 60 and 100 ka which have been well documented in other paleointensity records those features can be correlated to standard paleointensity curves with the aid of biogenic opal data and a radiolarian datum the mean sedimentation rates of the diatom rich cores collected in the eastern bering sea range from 10 to 20 cm kyr 1 in contrast the mean sedimentation rate of core bow 8a from the western edge of the bowers ridge is only 3 cm kyr 1 which is comparable to core es from the pelagic realm in the subarctic pacific these results suggest that biological productivity has been quite high during the late pleistocene in the eastern part of the bering sea but low over the western edge of the bowers ridge r 2005 elsevier ltd all rights reserved

environmental magnetic implications of greigite fe3s4 formation in a 3 m y lake sediment record from butte valley northern california authigenic greigite fe 3 s 4 has been identified in several horizons of lake beds in a 102 m core from butte valley northern california using mineral magnetic methods and x ray diffraction analysis the presence of greigite has several implications for the paleoenvironmental record from butte valley first its occurrence in 2 5 3 0 ma strata confirms that greigite can persist in the geological record for long periods of time second the detrital mineral magnetic record may be partially obscured by the presence of authigenic greigite and care must be taken in interpreting magnetic variations in the greigite bearing zones as paleoclimate proxies third differences in the timing of remanence acquisition for authigenic and detrital phases may compromise studies of high frequency geomagnetic field variations fourth greigite may also be significant as a paleoenvironmental indicator of lake and sediment chemistry the magnetic detection of greigite may therefore provide important information about paleolimnological conditions

petrographic characteristics of the solid fuels of india with particular reference to the coking coals abstract a summary is given of the available petrographic data on indian lignites and coals the latter categorised into coking semi caking and non coking fuels as delimited by vitrinite oil reflectances the coking coals form one fifth of the total solid fuel reserves in tertiary mesozoic and gondwana rock formations an attempt is made to establish the geological factors responsible for their genesis the tertiary lignites occur in the nichahom upper siwaliks neyveli miocene panandhro eocene kalol eocene and palana paleocene lignite fields they are of meso lignitous rank and composed mainly of huminite r m only the panandhro lignite being mainly of inertinite the tertiary coals of the jammu coalfields eocene are of hypoanthracitous rank and composed essentially of vitrinite r m 2 3 and fusinite the mesozoic coal deposit at ghuneri cretaceous mainly comprises vitrinite and subordinate inertinite and is of meta lignitous rank r m 0 52 the gondwana permian coals are composed of variable proportions of vitrinite and inertinite in the main and exinite in very minor amounts showing marginal variations from one coalfield to another and significant variations from one depositional basin to another the rank of the coals varies between meta lignitous and meso bituminous r m 0 42 1 45 evaluation of the permian coals indicates that the vitrinite oil reflectance determined in vitrinite rich coal is the main parameter for delineating predicting and assigning the coking properties many of the non coking coals have a maceral microlithotype composition which prevents the formation of good quality coke even from coal of suitable rank the proportion of vitrite and clarite together is higher than that of durite and fusite in the coking coals in the non coking coals the proportion of durite and fusite together exceeds that of vitrite and clarite and of the intermediates the semi caking coals are intermediate between the coking and non coking coals the vitrinite oil reflectance ranges from 0 85 to 1 50 in the coking coals from 0 70 to 0 85 in the semi caking coals and is less than 0 70 in the non coking coals the coking coals were formed at paleodepths exceeding 3 km other factors such as geological time being equal it is assumed that the petrographic composition of the coal is a function of the rate of subsidence of the basin thus the coking potential can be predicted from the knowledge of the geological history of the gondwana coal basins

the effect of deformation on the titaniq geothermobarometer an experimental study we performed high strain up to 47 axial compression experiments on natural quartz single crystals with added rutile powder tio2 and 0 2 wt h2o to investigate the effects of deformation on the titanium in quartz titaniq geothermobarometer one of the objectives was to study the relationships between different deformation mechanisms and incorporation of ti into recrystallized quartz grains experiments were performed in a griggs type solid medium deformation apparatus at confining pressures of 1 0 1 5 gpa and temperatures of 800 1 000 c at constant strain rates of 1 10 6 or 1 10 7 s 1 mobility of ti in the fluid phase and saturation of rutile at grain boundaries during the deformation experiments are indicated by precipitation of secondary rutile in cracks and along the grain boundaries of newly recrystallized quartz grains microstructural analysis by light and scanning electron microscopy the latter including electron backscatter diffraction mapping of grain misorientations shows that the strongly deformed quartz single crystals contain a wide variety of deformation microstructures and shows evidence for subgrain rotation sgr and grain boundary migration recrystallization gbmr in addition substantial grain growth occurred in annealing experiments after deformation the gbmr and grain growth are evidence of moving grain boundaries a microstructure favored by high temperatures electron microprobe analysis shows no significant increase in ti content in recrystallized quartz grains formed by sgr or by gbmr nor in grains grown by annealing this result indicates that neither sgr nor moving grain boundaries during gbmr and grain growth are adequate processes to facilitate re equilibration of the ti content in experimentally deformed quartz crystals at the investigated conditions more generally our results suggest that exchange of ti in quartz at low h2o contents which may be realistic for natural deformation conditions is still not fully understood thus the application of the titaniq geothermobarometer to deformed metamorphic rocks at low fluid contents may not be as straightforward as previously thought and requires further research

unraveling the mineralogical complexity of sediment iron speciation using sequential extractions author s slotznick sp sperling ea tosca nj miller aj clayton ke van helmond nagm slomp cp swanson hysell nl abstract 2019 american geophysical union all rights reserved iron speciation is one of the most widely applied proxies used to reconstruct oxygen levels and redox conditions in past aqueous environments the iron speciation proxy estimates proportions of different reactive iron species in fine grained sedimentary rocks which are mapped to redox conditions based on empirical calibrations from modern sediments it is based on a standardized extraction technique of sequentially applying acetate hydroxlamine hcl dithionite and oxalate solutions to a powdered sample in order to dissolve iron phases and quantify the amount of iron carried by carbonates easily reducible oxyhydroxides ferric iron oxyhydr oxides and magnetite respectively although tested on pure minerals and mixtures assessments of whether this sequential extraction process accurately dissolves the targeted minerals in natural sediments and sedimentary rocks are lacking in our study residues from each sequential extraction step were analyzed using rock magnetic and x ray diffraction experiments to identify and quantify the iron bearing minerals that were dissolved the dithionite extraction robustly removes the targeted mineralogy as magnetic data show it to solubilize nearly all of the goethite however magnetic quantification of magnetite was orders of magnitude less than the iron measured in the oxalate extraction x ray diffraction data suggest that dissolution of iron bearing clays specifically berthierine chamosite could explain this disparity our data compilation shows higher values of iron from the oxalate extraction in precambrian sedimentary rock samples suggesting a significant temporal shift in iron cycling recognition of heterogeneity in chemical extraction efficiency and targeting is vital for holistic multiproxy interpretation of past oxygen levels and communication between disciplines

rock magnetic signature of precipitation and extreme runoff events in south eastern patagonia since 51 200 cal bp from the sediments of laguna potrok aike a 106 m long sediment sequence from the maar lake laguna potrok aike in southern patagonia was recovered in the framework of the international continental scientific drilling program icdp potrok aike maar lake sediment archive drilling project pasado about half of the sedimentary sequence is composed of mass movement deposits mmds and the event corrected record reaches back to 51 200 cal bp here we present a high resolution rock magnetic study revealing two sedimentary facies associated with mmds and characterized by two different types of spurious gyroremanent magnetization grm acquired during static alternating field demagnetization the first rock magnetic signature is detected in mmds composed of reworked sand and tephra material the signature consists of grm acquired during demagnetization of the natural remanent magnetization nrm and other rock magnetic properties typical of iron sulfides such as greigite we interpret these intervals as authigenic formation of iron sulfides in suboxic conditions within the mmd the second rock magnetic signature consists of a series of 10 short intervals located on the top of mmds characterized by grm acquisition during demagnetization of the isothermal remanent magnetization irm based on geological limnological stratigraphic and climatic evidence these layers are interpreted as reflecting pedogenic hematite and or goethite brought to the lake by runoff events related to precipitation and permafrost melt the pedogenic iron minerals mobilized from the catchment most likely settled out of suspension on top of mmds after a rapid remobilization event the series of runoff events corresponds to periods of increased lacustrine productivity in laguna potrok aike and are coeval within the limit of the chronology to warm periods of the last glacial as recorded in antarctica the deglaciation in the mid latitudes of the southern hemisphere and enhanced precipitation during the early holocene in southeastern patagonia

a large gyromagnetic effect in greigite summary rotational and anhysteretic remanent magnetization rrm and arm acquisition curves of two sediment samples containing greigite have been measured up to peak fields of 80 mt at rotation frequencies between 5 and 95 revolutions per second rps at 95 rps the arm 70 mt direct field applied antiparallel to the rrm increased almost linearly with peak field but the rrm increased approximately exponentially the effective field bg defined in this case as 70rrrm arm was about 1100 mt for the two samples after the application of an alternating field af of 80 mt peak bg is approximately 10 times higher than previously observed for magnetite of size 1 mm although greigite is the dominant ferrimagnetic mineral present in these samples other studies snowball 1997a have shown that low concentrations of detrital multidomain magnetite are also present so that the high value of bg must be regarded as a lower limit unlike a magnetite sample that was used for comparison both greigite samples had a negative rrm at all rotation frequencies below 50 rps but like magnetite there was an increase in rrm when it changed from negative to positive at 50 rps in addition unlike magnetite the arm was not constant but approximately halved as the rrm became strong and positive above 50 rps arm antiparallel to rrm thus there appeared to be an interaction between the arm and the rrm further investigation of this interaction by applying weak direct fields parallel and then antiparallel to the rrm 80 mt peak af 95 rps rotation rate showed that the arm was linear with direct field but was indeed always smaller when the direct field producing it was antiparallel to the rrm at present it is not clear why gyromagnetic remanences are so strong in greigite such high values of bg have never been observed before except in the very special case of a self reversing lithium chromium ferrite near its moment compensation temperature these high values of bg might enable rrm to be used as an indicator for greigite if they turn out to be unique to this mineral

new discoveries of coal in mozambique development of the coal resource estimation methodology for international resource reporting standards abstract the coal in mozambique s tete province has been known about for a long time as the artist explorer thomas baines first captured onto canvass a coal outcrop on the banks of the zambezi in the late 1850s the first geological works in the tete province referred to the studies of coal occurrence and were undertaken by richard thornton 1859 a geologist on the zambezi expedition under dr david livingstone and guyot however most of the recent exploration has been conducted to ascertain the economic potential of the coal resources within the region the majority of these resources are located within remnants of the ecca group of rocks of the karoo supergroup in the zambezi graben of the tete province of mozambique the coalfield consists of various sub basins and is considered the largest undeveloped coal province in the world amongst others it forms host to the well publicised moatize metallurgical and thermal coal deposit reported to contain 2 4 gt of coal and located within the moatize sub basin in late 2004 a consortium of companies headed by brazilian iron ore miner vale won the right to develop the moatize coal deposit other companies which tendered for this right were bhp billiton rio tinto and anglo american vale is partnered in this project with american metals and coal international amci a north american coal producer which owns 5 of the consortium the consortium bid 122 8 m for the rights to explore and develop the coal deposit the allocation of the tender award to vale opened the way for smaller investors such as the zambezi energy corporation zec who decided in late 2004 to develop a number of projects within licence blocks in the zambezi graben investment within the region has accelerated rapidly over the last couple of years and the region has seen a number of developments during this time the authors have helped to develop the potential of new coal resources and have modified the traditional coal resource estimation techniques such that they can be used for reporting coal resources according to the terminology and guidelines given in the jorc the joint ore reserves committee code jorc 2004 the paper describes the complexities of the underlying regional and local resource geology and describes the challenges of producing resource estimates to international standards such as jorc

rock magnetism and palaeomagnetism of greigite bearing mudstones in the italian peninsula magnetic measurements were carried out on a collection of samples from different geological settings throughout the italian peninsula the samples display magnetic properties that indicate the presence of ferrimagnetic iron sulphide minerals paired samples were also investigated to compare the palaeomagnetic behaviour with respect to different demagnetization treatments thermal static and tumbling alternating field af demagnetization greigite fe3s4 was positively identified in most samples in agreement with previous studies of greigite the sediments display thermal decomposition of the magnetic carriers at temperatures above ca 230 c resulting in decreased magnetic susceptibility values and maximum unblocking temperatures tub mostly in the range 320 350 c high saturation isothermal remanent magnetization sirm to low field magnetic susceptibility k ratios sirm k 10 ka m hysteresis ratios that are typical for single domain sd grains mrs ms 0 5 and b0 cr b0 c 1 5 where mrs is the saturation remanence ms is the saturation magnetization b0 c is the coercive force and b0 cr is the coercivity of remanence moderate coercivity with b0 cr values that range between 52 and 81 mt and a tendency to acquire a significant rotational remanent magnetization rrm we also found that greigite bearing sediments are particularly sensitive to field impressed anisotropy we propose a new magnetic parameter that can be used as a rapid mean to screen a rock sample for the presence of greigite which relies on its sd behaviour in field impressed anisotropy experiments in greigite bearing sediments the magnetic susceptibility measured in a given direction is increased by the application of a relatively high magnetic field 0 9 t in our experiments at right angles to this direction the susceptibility increase is directly correlated to the concentration of greigite in the sediment the comparative palaeomagnetic analysis of standard demagnetization techniques indicates that thermal demagnetization in close steps up to 350 380 c is clearly the most effective treatment for the isolation of the remanent magnetization carried by greigite whereas af demagnetization treatments display significant acquisition of unwanted magnetic remanences gyroremanent remanent magnetization grm and rrm at fields above ca 40 mt

magnetic hysteresis properties of greigite fe3s4 and a new occurrence in holocene sediments from swedish lappland a new occurrence of ferrimagnetic greigite fe3s4 is reported in freshwater holocene sediments from gaskkamus gorsajavri in swedish lappland the presence of greigite was inferred from the mineral magnetic analysis of sediment cores the greigite bearing sediments possess a high saturation isothermal remanent magnetisation to susceptibility sirm ratio a characteristic shared by other natural sediments known to contain greigite the hysteresis properties measured using a vibrating sample magnetometer of natural greigite extracted from lake sediments show much higher saturation coercivity b0 c and mrsms ratio values approximately 50 mt and 0 5 respectively than synthetic samples of greigite approximately 12 mt and 0 2 the results suggest that synthetic greigite samples contain crystals ranging from small non remanence carrying superparamagnetic grains to large multi domain grains in contrast the natural samples probably consist predominantly of pseudo single domain and single domain crystals capable of carrying a chemical remanent magnetisation however the unstable nature of greigite under laboratory conditions creates difficulty in characterising its physical attributes

the karoo basin of south africa type basin for the coal bearing deposits of southern africa abstract the coal bearing sediments and coal seams of the karoo basin southern africa are described and discussed the karoo basin is bounded on its southern margin by the cape fold belt onlaps onto the kaapvaal craton in the north and is classified as a foreland basin coal seams are present within the early permian vryheid formation and the triassic molteno formation the peats of the vryheid formation accumulated within swamps in a cool temperate climatic regime lower and upper delta plain back barrier and fluvial environments were associated with peat formation thick laterally extensive coal seams have preferentially accumulated in fluvial environments the coals are in general inertinite rich and high in ash however increasing vitrinite and decreasing ash contents within seams occur from west to east across the coalfields the triassic molteno coal seams accumulated with aerially restricted swamps in fluvial environments these molteno coals are thin laterally impersistent vitrinite rich and shaly and formed under a warm temperate climatic regime palaeoclimate depositional systems differential subsidence and basin tectonics influence to varying degrees the maceral content thickness and lateral extent of coal seams however the geographic position of peat forming swamps within a foreland basin coupled with basin tectonics and differential subsidence are envisaged as the primary controls on coal parameters the permian coals are situated in proximal positions on the passive margin of the foreland basin here subsidence was limited which enhanced oxidation of organic matter and hence the formation of inertinitic coals the coals in this tectonic setting are thick and laterally extensive the triassci coals are situated within the tectonically active foreland basin margin rapid subsidence and sedimentation rates occurred during peat formation which resulted in the preservation of thin laterally impersistent high ash vitrinite rich shaly coals

deposition rates and 14c apparent ages of holocene sediments in the bothnian bay of the gulf of bothnia using paleomagnetic dating as a reference abstract three 6 m long cores of sediments were collected in the northern middle and southern part of the bothnian bay the sediments were dated by paleomagnetic dating techniques constrained by magnetic properties and geochemical data the results indicate the ages of the sediments in the bottom part of the cores in the northern middle and southern parts of the bothnian bay to be approximately 5300 years bp 5350 years bp and 3500 years bp respectively the deposition rate calculated from the estimated ages at various depths show that the deposition rate was generally in the range 0 5 1 5 mm year but it was higher in the southern part than in the middle and northern parts of the bay there was a significant increase in the deposition rate at ca 2200 years bp recorded in all three cores a rate varying between 2 47 and 3 07 mm year and lasting until ca 1840 years bp a proposed constant uplift rate of the crust during the period ca 5500 years bp to present is thus not reflected by a constant deposition rate the peaks in deposition rates at ca 2200 1840 years bp were followed by a decrease in salinity this phenomenon is suggested to be caused by crustal uplift with a threshold being formed in the southern part of the bay thereby increasing the reactivation of bottom sediments and reducing the inflow of brackish water from the bothnian sea the 14c ages of the sediments reveal differences in age compared with the paleomagnetic ages in the southern core the 14c ages are ca 1350 years older and in the north the age offset is mixed the reactivation and re deposition of sediments is argued to be the reason for the apparent 14c age differences this finding demonstrates that 14c cannot be used for the dating of bothnian bay sediments unless the radiocarbon age offset has been determined

magnetic discrimination of pyrrhotite and greigite bearing sediment samples by using bulk samples rock magnetic measurements were performed to discriminate between pyrrhotite and greigite bearing shallow marine sediments that are now uplifted above sea level in southwestern taiwan thermal demagnetization of a composite isothermal remanent magnetization irm was found to be effective in differentiating between the two types of sediments to check the thermal instability and estimate the true unblocking temperature tb spectra of sediments containing these minerals saturation irms sirms were imparted at each temperature step during demagnetization while pyrrhotite bearing samples showed unambiguous tb temperature spectra greigite bearing samples underwent considerable alteration which is responsible for most of the decrease in magnetization during thermal demagnetization such thermal instability of greigite is a practical and important clue for its identification zero field warming of irm from 5 to 300 k sensitively indicates the presence of pyrrhotite and trace magnetite in bulk samples without any magnetic separation

strain partitioning across a subduction thrust fault near the deformation front of the hikurangi subduction margin new zealand a magnetic fabric study on iodp expedition 375 site u1518 abstract understanding the distribution of strain along thrust and splay faults in active accretionary systems is crucial to understand the mechanical properties of the sediments and the strength of the fault zone and its slip behavior this paper investigates the distribution of strain through sediment compaction and texture development across the p paku fault a major splay fault near the deformation front of the hikurangi subduction margin new zealand using the anisotropy of magnetic susceptibility technique ams international ocean discovery program site u1518 penetrated hanging wall fault zone and footwall sequences to a maximum depth of 484 9 meters below seafloor a total of 330 discrete samples was subjected to ams measurements and magnetic remanence data used to reconstruct the axial orientation of each sample in a geographic reference frame the ams display distinct fabric differences between hanging wall through the fault zone and footwall domains demonstrating that strain is partitioned across the fault zone hanging wall sequences show a strike parallel northeasterly lineation of kmax and weakly prolate shapes typical for a component of northeast southwest lateral shortening in contrast footwall sequences are more oblate and show a clustering of kmax in northerly direction this demonstrates that strain in the footwall is dominated by gravitational loading however a component of sub horizontal east westerly strain parallel to the convergence direction of the pacific plate exists strain decoupling between hanging and footwall sequences occurs near the top of the p paku fault zone differences in the degree of magnetic susceptibility between footwall sediments incorporated into the fault zone and the underlying undeformed footwall sequences are indicative for the progressive dewatering of the underconsolidated footwall sequences

paleodepositional environments and tectonosedimentary controls of the postglacial permian coals karoo basin south africa abstract coal deposits of the karoo basin in south africa are contained within an 80 250 m thick clastic sequence designated the vryheid formation this formation constitutes part of the ecca group of the karoo sequence and contains several mineable bituminuos coal and anthracite beds and sporadic coking coal seams the sedimentary succession was deposited during the early permian following the late carboniferous dwyka ice age paleoclimate initially influenced the paleodepositional environments which for the lowermost stages comprised glaciofluvinal outwash braided plain deposits overlying minor deltaic and glaciolacustrine fill the early permian floral assemblages attest to a cool temperature climatic regime in the extreme northern parts of the basin the lowermost coals frequently directly overlie dwyka diamictite or pre karoo basement paleodepositional systems associated with the coals above the glaciogenic succession consisted predominantly of regressive fluviodeltaic facies assemblages in the northern regions regressive deltaic lobes prograded rapidly basinward across the relatively shallow intracratonic platform in the northeast areas greater subsidence rates were accompanied by multiple stacking of regressive deltaic cycles in several areas of the coalfields peat accumulation was associated with the bed load braided fluvial systems these subsequently modified the underlying deltaic deposits by intense and deep erosion that removed portions of the underlying stratigraphy smaller scale syndepositional anastomosed rivers which were contemporaneous with certain peat swamps locally controlled seam distribution and adversely affected coal seam quality coal distribution was directly controlled a the tectonic setting b the nature of the pre karoo basement lithologies c the basement paleotopography and d the paleodepositional systems associated with and following peat formation the coalfields are restricted to a relatively small area in the northern and northeastern parts of the karoo basin where a stable intracratonic shelf provided a suitable tectonic setting for peat accumulation resistant basement lithologies orthoquartzite and felzite produced positive topographic relief while easily weatehred archean granite basement terrain left residual topographic depressions that were later extensively filled by sediment differential compaction of fine sediment mud and silt deposited over the diverse basement topography provided further subtle controls on coal seam thickness sediments and coal overlying basement highs compacted significantly causing thinning and a draping effect of the sedimentary cover in contrast paleovalleys contained substantial thickness of sediment and host some of the thickest seams these coals can however thin and shale out against the adjacent elevated valley flanks the paleovalley coals were further affected by multiple seam splits produced by fluvial channels that contemporaneously occupied the lowland areas

the detection of single domain greigite fe3s4 using rotational remanent magnetization rrm and the effective gyro field bg mineral magnetic and palaeomagnetic applications summary the intensity of rotational remanent magnetization rrm acquired by single domain greigite at a rotation frequency of 5 rps was combined with measurements of anhysteretic remanent magnetization arm to calculate the effective biasing field bg that produced the rrm samples of single domain greigite had bg values between 137 and 84 t and a mdfrrm of c 80 mt by contrast a suite of natural and synthetic ferrimagnetic iron oxide samples including single domain magnetite and yfe3o4 tape particles acquired bg values between 3 and 14 t and mdfrrm ranged between 43 and 68 mt when rrm was acquired multidomain magnetite did not acquire a rrm bg values at 5 rps were calculated from previously published data for magnetite particles of different grain sizes which revealed a minimum bg value of 24 t and a mdfrrm of 57 mt for the finest fraction 0 2 0 8 m in diameter in a geological example measurements of bg and mdfrrm were used to detect the presence of greigite in a 4 m long late weichselian sediment core variations in inclination declination and the intensity of the natural remanent magnetization nrm correlate with changes in magnetic mineralogy

gyroremanent magnetization and the magnetic properties of greigite bearing clays in southern sweden summary the acquisition of a gyroremanent magnetization grm by single domain sd greigite particles during alternating field af demagnetization is demonstrated previous palaeomagnetic studies failed to identify the presence of authigenic greigite in the glacio marine clays studied these clays formed the subject of an earlier debate about the validity of a late weichselian geomagnetic excursion the gothenburg flip in southern sweden the greigite carries a stable chemical remanent magnetization crm which coexists with a detrital remanent magnetization drm carried by magnetite af demagnetization could not isolate the primary remanence in the sediments where magnetite and greigite coexist due to the overlapping coercivity spectra of the two minerals and the inability to determine the time lag between sediment deposition and crm formation thermal demagnetization removed the crm at temperatures below 400 dc but this method was hindered by the unconsolidated nature of the sediments and the formation of secondary magnetic minerals at higher temperatures the results suggest that the low coercivity drm carried by magnetite was mistaken for a viscous component in the earlier studies hence the former debate about the record of the gothenburg flip may have been based on erroneous palaeomagnetic interpretations or non reproducible results af demagnetization procedures applied to samples suspected of bearing sd magnetic particles such as greigite should be carefully selected to recognize and account for grm acquisition

a record of reversed polarity carried by the iron sulphide greigite in british early pleistocene sediments abstract palaeomagnetic measurements were made on samples extracted from a short sequence of early pleistocene estuarine clays now exposed in a sea cliff near sheringham on the north norfolk coast uk on the basis of earlier palynological work these clays had been ascribed a pastonian late tiglian age the clays show marked changes in colour from reddish brown at the top of the unit to blue grey in the middle and grey brown at the base the palaeomagnetic data vary in close association with these colour changes the top and basal brown clays show scattered normal directions of low intensity while the middle blue clays show strongly clustered reversed directions of much higher intensities some samples taken from the boundary between the middle blue and upper red clays show upon demagnetisation a normal overprint on a stable reversed polarity using high gradient magnetic extraction magnetic concentrates have been obtained from the strongly magnetic middle blue clays the presence of iron sulphide minerals in these concentrates was identified using energy dispersive x ray analysis during scanning electron microscopy more specifically x ray diffraction identifies greigite as the only detectable ferrimagnetic mineral in the magnetic concentrates rock magnetic measurements show clear qualitative differences in the magnetic mineralogies of the three clay subunits but absolute identification of the magnetic mineralogy of the weakly magnetic upper and basal brown clays has not yet been possible we interpret the sequence as a primary reversed polarity record this record is carried by the iron sulphide greigite as a chemical remanence acquired during syn depositional reduction of iron via the decomposition of organic material in these anoxic tidal clays subsequently the upper and basal subunits of the clay have been oxidised by permeation of groundwater from the adjacent coarse grained sediments most of the griegite in the oxidised margins of the clay has been altered as a result to a new less efficient magnetic recording material which thus carries a later scattered low intensity normal overprint

rotational remanent magnetization rrm and its high temporal and thermal stability summary the time and temperature stability of various types of magnetic remanence has been measured in pottery samples containing magnetite and in a clay sample containing manganese ferrite the time decay of rotational remanent magnetization rrm anhysteretic remanent magnetization arm and a low field isothermal remanent magnetization irm has been measured while the decay of the last two remanences is easily measurable at about 2 and 19 per cent per decade of time respectively the decay of rrm is too small to be measured being less than about 0 1 per cent per decade of time thermal demagnetization of thermoremanent magnetization trm arm and rrm indicates that rrm is also the most thermally stable the implications of these experiments are that rocks which exhibit gyromagnetic effects such as rrm contain highly stable particles and therefore are likely to be most suitable for palaeomagnetism

petrographic characteristics and carbon isotopic composition of permian coal implications on depositional environment of sattupalli coalfield godavari valley india abstract the present paper entails a study carried out on selected samples of coal and carbonaceous shales of permian age from the sattupalli open cast coal mine of godavari valley andhra pradesh to know their petrographic and chemical characteristics based on these characteristics the depositional environment has also been discussed the study reveals that these coals are sub bituminous in rank and are chemically characterized by low to medium moisture 4 3 to 8 6 wt and volatile matter 24 5 to 32 6 wt while the ash yield varies between 16 4 and 35 3 wt petrographically these coals are rich in inertinite liptinites occur in very small concentration collotelinite collodetrinite and vitrodetrinite are the main vitrinite macerals whereas fusinite inertodetrinite and semi fusinite constitute the major proportion of inertinites mean 13c value measured for coal is 22 58 0 20 and for carbonaceous shale it is 23 64 0 57 while in the organic matter of barakar sandstones the 13c is 25 2 2 1 dry periods are reflected by the abundance of inertinite in some samples while more anoxic conditions are indicated by high concentration of vitrinite in some samples seam ii of sattupalli coalfield initially formed in dry condition and gradually flooding took place due to rise in the water table during the formation of the upper part of the seam again a relatively dry phase prevailed moreover a positive correlation of 13corg with toc and a negative one with tic indicate that 13corg is being modified by 13cdic

alternating field demagnetization of rocks and the problem of gyromagnetic remanence abstract alternating field a f demagnetization has proved to be a very reliable technique for separating the magnetization components of rock samples the method is subject to errors caused by either imperfection of the technique or by intrinsic properties of a rock recently stephenson 1 2 introduced the term gyroremanent magnetization grm for a disturbing remanent magnetization that can be acquired by magnetic material during tumbling or stationary a f demagnetization the implications for the routine a f demagnetization of anisotropic rock samples seemed to be very serious here however a method is presented on how to avoid the effect of grm on results obtained from stationary a f demagnetization

gyromagnetic remanence acquired by greigite fe3s4 during static three axis alternating field demagnetization summary a magnetic study was carried out on lacustrine sediments from the zoigebasin tibetan plateau in order to obtain a better understanding of palaeoclimatic changes there gyromagnetic remanence grm acquisition is unexpectedly observed during static three axis alternating field af demagnetization in about 20 per cent of a large number of samples x ray divraction xrd analysis on a magnetic extract clearly shows that greigite is the dominant magnetic mineral carrier scanning electron microscopy sem reveals that the greigite particles are in the grain size range of 200 300 nm possibly in the single domain state greigite clumps of about 3 mm size are sealed by silicates fitting of xrd peaks yields a crystalline coherence length of about 15 nm indicating that the particles seen in the sem are polycrystalline grm intensities of most samples are of the same order as the nrm while others show much stronger grm although their magnetic properties are similar variation of the demagnetization sequence confirms that grm is mainly produced perpendicular to the af direction the anisotropy direction can be derived from grm but more systematic studies are needed for detailed conclusions an attempt to correct for grm failed due to high grm intensities and because smaller grm acquisition was also found along the demagnetization axis behaviours of acquisition and af demagnetiz ation of grm are comparable with those of nrm arm irm indicating fine grain sizes of remanence carriers

magnetostratigraphy of drill core sg 1b in the western qaidam basin ne tibetan plateau and tectonic implications the qaidam basin is an ideal archive to study long term climate and erosion histories at the ne tibetan plateau we present a magnetostratigraphic study of the 723 m deep drill core sg 1b of lacustrine sediments at the jianshan anticline in the western qaidam basin the polarity sequence shows 18 normal and 19 reverse polarity zones which can be readily correlated with chrons c1n c3br of the geomagnetic polarity time scale 2004 gpts 2004 dating the core at about 7 3 1 6 ma the resulting mean sediment accumulation rate sar between polarity boundaries ranges from 6 5 to 30 4 cm ka 1 high sars occur within the intervals of 7 3 6 0 5 2 4 2 and 3 6 2 6 ma indicating three episodic phases of higher erosion from the derived variation of sars and previous results we conclude that growth strata at the jianshan anticline started to develop at similar to 1 6 ma by limb rotation all this we relate to pulse tectonic uplift of the ne tibetan plateau and fault propagation folding in the qaidam basin

deglaciation sequences in the permo carboniferous karoo and kalahari basins of southern africa a tool in the analysis of cyclic glaciomarine basin fills the late westphalian to artinskian glaciomarine deposits of the karoo and kalahari basins of southern africa consist of massive and stratified diamictite mudrock with ice rafted material sandstone silty rhythmite shale and subordinate conglomerate forming a cyclic succession recognizable across both basins a complete cycle comprises a resistant basal unit of apparently massive diamictite overlain by softer bedded stratified diamictite sandstone and mudrock with a total thickness of as much as 350 m four major cycles are observed each separated by bounding surfaces lateral facies changes are present in some cycles the massive diamictites formed as aprons and fans in front of the ice grounding line whereas the stratified diamictites represent more distal debris flow fans the sandstones originated in different environments as turbidite sands small subaqueous outwash channel sands and delta front sands the rhythmites and mudrock represent blanket deposits derived from turbid meltwater plumes cycles represent deglaciation sequences which formed during ice retreat phases caused by eustatic changes in the karoo and kalahari basins evidence for shorter term fluctuation of the ice margin is present within the major advance retreat cycles hardly any sediment was deposited during lowstand ice sheet expansion whereas a deglaciation sequence was laid down during a sea level rise and ice margin retreat with the volume of meltwater and sediment input depending on temporary stillstands of the ice margin during the retreat phase the duration of the cycles is between 9 and 11 ma suggesting major global tectono eustatic events smaller cycles probably linked to orbital forcing were superimposed on the longer term events a sequence stratigraphic approach using the stacking of deglaciation sequences with the ice margin advance phases forming bounding surfaces can be a tool in the framework analysis of ancient glaciomarine basin fills

a study of gyroremanent magnetisation grm and rotational remanent magnetisation rrm carried by greigite from lake sediments summary further studies of gyroremanent magnetisation grm and rotational remanent magnetisation rrm have been conducted on lake sediments from the zoige basin in the eastern tibetan plateau in which greigite is the main carrier of gyroremanent magnetisation greigite has the greatest effective gyrofield bg of all magnetic minerals studied so far being several hundred t for a peak af of 80 mt this high bg value has the potential to be used as an indicator for greigite the grm produced during static alternating field af demagnetisation became close to its maximum at a peak af of 150 mt attempts to extract the natural remanent magnetisation nrm by algebraic elimination of the grm were unsuccessful above fields of about 30 mt because the grm became much larger than the remaining nrm the grm of a crushed sample was much reduced because of the destruction of the sample s anisotropy although as expected both rrm and bg were similar before and after crushing thus demonstrating that rrm and bg are independent of anisotropy measurement of the anisotropy of two samples from different depths showed that the deeper sample which acquired the higher grm also had the higher anisotropy presumably as a result of greater sediment compaction study of anisotropy of grm may help to elucidate the preferred alignment of greigite within the sample which is difficult to ascertain by other means

evidence of late gelasian dispersal of african fauna at coste san giacomo anagni basin central italy early pleistocene environments and the background of early human occupation in europe since the late 70s the early pleistocene gelasian site of coste san giacomo anagni basin central italy has been known amongst palaeontologists for its diverse vertebrate fauna during the last 5 years new excavations and the drilling of a 46 m deep core have provided novel pieces of information palaeomagnetic data pollen and small vertebrates analyses are presented here for the first time and combined with the updated list of the large vertebrates and ostracod analysis in a multidisciplinary perspective large and small mammals pollen and ostracod analyses have allowed an integrated palaeoenvironmental reconstruction of the sedimentary sequence depicting the evolution of the alluvial plain in the surrounding landscape moreover magnetostratigraphy pollen and small mammal biochronological data have confirmed the position of the coste san giacomo faunal unit focusing the possible age of the mammal assemblage around 2 1 ma in a reversed phase before the base of the olduvai chron in particular the occurrence of the large vole mimomys pliocaenicus has important biochronological significance the coste san giacomo site offers a unique opportunity to investigate the faunal and environmental changes that occurred in mediterranean europe during the early pleistocene coinciding with major climatic changes at a global scale the occurrence of taxa such as hippopotamus sp in the assemblage provides evidence of early dispersal events of african taxa prior to the early homo diffusion into europe

the lacustrine section at lukundol kathmandu basin nepal dating and magnetic fabric aspects abstract the fluvial and lacustrine sediments of kathmandu basin in central nepal are a good archive to study the past environmental changes and the history of development of the sw indian monsoon a sequence of about 170 m exposed at the southern part of the basin is divided into two lithological units lukundol formation and itaiti formation the lukundol formation mainly comprises fine grained sediments whereas gravel beds dominate the itaiti formation in total 750 oriented samples were collected all along the accessible part of the sequence in 10 cm3 plastic boxes with a sampling interval of 10 cm additional 128 samples were collected for pollen analysis with a sampling interval of 50 cm magnetostratigraphy is established based on four magnetic transitions indicating that the sampled section spans 0 75 1 1 ma amino acid dating on a fossil found in a lignite layer at 88 m yields an age of 0 8 1 0 ma is consistent with the age derived from magnetic polarity stratigraphy anisotropy of magnetic susceptibility ams measured in 250 samples spanning the whole section reveals a sedimentary fabric with nw se oriented maximum directions lithological changes are significant at 67 5 m above which thick gravel beds appear and imply significant change in the depositional regime mainly two magnetic components are identified magnetite dominant all along the whole sequence and hematite relatively more important at depths with lower susceptibility

magnetic enhancement of baltic sea sapropels by greigite magnetofossils magnetotactic bacteria mtb are known to biosynthesise single domain magnetite fe3o4 for geomagnetic navigation and their relict magnetosomes called magnetofossils can control the magnetic properties of lake and marine sediments magnetotactic bacteria also produce greigite fe3s4 magnetosomes but compared to those made of magnetite relatively little is known about the sedimentary environments where they are produced and the magnetic properties of the preserved particles we studied the magnetic properties of sediment cores from two basins the north central baltic proper and eastern gotland basin that currently experience hypoxia and we discovered the magnetic enhancement of older laminated sapropels which are a signal of past occurrences of anoxia and hypoxia in the baltic sea magnetic concentrates extracted from the laminated sapropels were characterised by transmission electron microscopy and energy dispersive x ray spectrometry and we identified only single domain greigite fe3s4 particles with a mean size of 55 75 nm which we interpret as magnetofossils due to diagnostic chains of individual particles separated by an intact dividing membrane the degree of magnetic enhancement in the laminated sapropels has a positive relationship with loss on ignition data which indicates a link between the production of greigite magnetosomes organic matter supply and preservation and redox conditions the coercive force of collections of non interacting greigite magnetofossils is 13 mt which is considerably lower than the magnetite counterparts 30 mt and strictly non bacterial and larger greigite single domain grains 60 mt the values of the interparametric ratios of sirm w warm sirm and warm w that we obtain for our greigite magnetofossils overlap with those previously considered to be diagnostic of magnetosomal magnetite the presence of bacterial greigite which is easily detected by magnetic measurements forms a proxy for hypoxia and anoxia thus aiding the palaeoenvironmental interpretation of how oxygen conditions in the baltic sea have changed over time

the geology petrology palynology and geochemistry of permian coal basins in tanzania 2 songwe kiwira coalfield abstract this study provides coal quality petrological palynological and geochemical rock eval data on permian coal seams and associated shales and mudstones of the karoo supergroup of the songwe kiwira coalfield tanzania the coal seams which have a cumulative thickness of 6 80 m occur in the shale coal sandstone facies of the mchuchuma formation of artinskian to kungurian age coal quality data calorific values volatile matter contents and vitrinite reflectances indicate high volatile c bituminous to high volatile a bituminous coals having relatively high ash yields 22 49 wt and highly variable sulphur contents 0 17 9 2 wt they could be used to fuel small scale power generation units thereby providing electricity to nearby towns and villages also the coals could be used as a substitute for wood which is becoming increasingly scarce in rural tanzania charcoal is still the main energy source for cooking and wood is used extensively in brick kilns and for making roofing tiles petrological analysis indicated that the coals are dominated by dull to banded dull lithotypes with seams at the base of the mchuchuma formation enriched in inertinite macerals up to 83 vol whereas up section vitrinite contents increase palynological analyses indicated that the assemblage in the lower mchuchuma formation scheuringipollenites assemblage is dominated by trilete spores whereas in the remainder of the section non taeniate disaccates dominate scheuringipollenites protohaploxypinus assemblage facies critical macerals suggest for most seams a marsh wet forest swamp depositional setting which is consistent with the palynological data rock eval analyses indicate type ii iii kerogen with tmax c values ranging from 426 to 440 corresponding to the early stage of hydrocarbon generation thermal alteration indices 2 to 2 and vitrinite reflectance levels 0 60 0 83 ro support the rock eval maturity assessment and despite the predominance of terrestrial derived organic matter there is evidence of oil generation and expulsion in the form of cavity and fracture filling exsudatinite

flow structures and mineralisation in thermally altered coal from the moatize basin mozambique abstract this paper examines changes in structural and petrographic characteristics of organic and inorganic matter developed in a cored 35 m thick permian coal seam from the moatize basin mozambique in proximity to an early jurassic intrusive igneous body megascopic and microscopic examinations of hand samples and polished blocks respectively were carried out to characterise the deformation and petrographic changes of the coal sem eds analysis was used for mineral identification and modes of occurrence the upper part of the core is thermally altered exhibiting intense megascopic folding of the bedding at microscopic level vitrinite presents an incipient mosaic coke texture semi coke whereas fusinite and semifusinite layers are deformed exhibiting folded structures coal petrographic characteristics suggests the temperature in the coal at this location reached no higher than 400 c but was enough for softening and ductile deformation of bands to occur apart from epigenetic chamosite occurring exclusively in the upper section and monazite that appears only in the lower section of the core microscopic studies showed similar distribution of the mineral species in both sections of the seam except with a change in their mode of occurrence detrital or syngenetic minerals in the lower section of the seam occur also as epigenetic in the thermally affected upper section siderite occurs as syngenetic nodules in the lower section but appears as epigenetic fracture filling developed with the cooling of the organic material in the upper section quartz occurs as detrital grains in the lower section whereas in the upper section this mineral occurs also as an epigenetic euhedral mineral filling the fracture system fluorapatite occurs as detrital syngenetic and euhedral epigenetic the mineralisation in the fractures also gives indications about the fluid circulation associated with the magmatic intrusion at least three stages of hydrothermal fluids were distinguished from the first to the last stage a p f and si rich fluid an fe ca mg rich fluid and an al si rich fluid these fluids gave origin to the minerals in the fractures and to some of the minerals inside the cell lumina of the inertinite macerals given the euhedral shape of some of the epigenetic minerals there was sufficient time for them to grow into euhedral forms

rock magnetism of greigite bearing sediments from the dead sea israel summary detailed magnetostratigraphic investigations were carried out on five sediment cores obtained from three sites on the northwestern shore of the dead sea israel the sediments are heterogeneous composed of fine clastic layers alternating with authigenic aragonite the magnetic remanence is carried by ti magnetite and greigite reflecting a detrital as well as an authigenic phase directions of the characteristic remanent magnetization were obtained from stepwise af demagnetization of the natural remanent magnetization and subsequent principle component analysis the acquisition of a gyroremanent magnetization in a noticeable amount of the samples could be linked to core disturbances the depth age models based on ams 14c datings on plant remains yielded an age of 10 04 ka cal bp for the base of the longest profile from site ein gedi a continuous lacustrine sediment sequence the profiles from the two other sites representing near shore sedimentation are interrupted by a hiatus in sedimentation comparison of the inclination and declination records from all dead sea cores and nearby sited lakes suggest that low frequency variations documented in the dead sea sediments are likely of geomagnetic origin

geology of barcode type coking coal seams mecondezi sub basin moatize coalfield mozambique abstract the geology of barcode type coking coal seams including basin setting stratigraphy sedimentary facies coal forming environments seam morphology and implications for exploitation in the mecondezi sub basin moatize coalfield mozambique is presented the moatize coalfield is located along the zambezi valley gondwana rift that developed over heterogeneous precambrian basement in between the zambia and zimbabwe cratons basement heterogeneities controlled basin development coal seams occur in a kilometer thick lower karoo succession classified into vuzi and moatize formations of late carboniferous to permian age coal seam stratigraphy in ascending order shows six seams namely the sousa pinto chipanga bananeiras intermedia grande falesia and andre the grande falesia seam has attained a maximum thickness of up to 250 m making it one of the thickest coal seams known so far in the world based on sedimentary attributes the lower karoo coal succession is classified into three facies assemblages named vuzi transitional and moatize the karoo sedimentation commenced with the deposition of tillite diamictite and rhythmite of vuzi assemblage over precambrian basement in periglacial environments during the late carboniferous the succeeding transitional assemblage is characterized by the presence of coal beds in association with diamictite thereby signaling the onset of coal forming environments during the interludes of glacial retreat the moatize assemblage includes coal seams mudstone rhythmite and sandstone deposited in delta plain mire environments coal seam morphology is barcode in type and characterized by cyclic stacking pattern of thin beds of coal carbonaceous mudstone and mudstone high ash contents of the coal are attributed to flooding of low level mires and ground water fluctuations in a tectonically unstable basin setting the coal is bituminous vitrinite rich medium to high volatile and medium in rank as a coking coal it compares well with some of the coking coals of limpopo area in south africa constraints on exploitation of barcode type coal seams are linked to barcode morphology which can be overcome by selective mining of coal

south africa s coalfields a 2014 perspective abstract for well over a century and a half coal has played a vital role in south africa s economy and currently bituminous coal is the primary energy source for domestic electricity generation as well as being the feedstock for the production of a substantial percentage of the country s liquid fuels it furthermore provides a considerable source of foreign revenue from exports based on geographic considerations and variations in the sedimentation origin formation distribution and quality of the coals 19 coalfields are generally recognised in south africa this paper provides an updated review of their exploration and exploitation histories general geology coal seam nomenclature and coal qualities within the various coalfields autocyclic variability is the norm rather than the exception whereas allocyclic variability is much less so and allows for the correlation of genetically related sequences during the mid jurassic break up of gondwana most of the coal bearing successions were intruded by dolerite these intrusions are important as they may cause devolatilisation and burning of the coal create structural disturbances and related seam correlation problems and difficulties in mining operations whilst many of the coalfields have been extensively explored and exploited those in the north of the country have until recently received much less attention four coalfields occur partly or wholly within the limpopo province of south africa and these may contain as much as 70 of south africa s remaining coal resources these coalfields in particular have been the focus of recent exploration due to the presence of large coking and thermal coal resources as well as for their coal bed methane potential and these resources need to be unlocked with regards to creating maximum benefit and minimal environmental degradation south africa s coals have also been recently addressed as palaeoclimate archives recording gondwana s postglacial climate amelioration by major changes in land plant communities and proving high resolution palyno stratigraphy as a crucial tool to decipher climate change during the permo carboniferous this aspect of the coals of south africa is also reviewed

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals

evolution of pennsylvanian late carboniferous peat swamps of the ruhr basin germany comparison of palynological coal petrographical and organic geochemical data abstract this study focuses on the reconstruction of the environment during peat swamp development eight coal and sedimentary organic rock bearing seam successions were examined all belonging to the duckmantian pennsylvanian late carboniferous 410 samples were analysed with coal petrographical methods 155 of these also by palynological methods in addition on 55 samples organic geochemical investigations were carried out with respect to n alkanes and iso alkanes the established coal petrographical parameters gelification index gi tissue preservation index tpi groundwater index gwi and vegetation index vi were used to characterize different periods of peat swamp development furthermore the new index wci water cover index was introduced to reflect water level conditions by using the ratio between hydrophilous hygrophilous and mesophilous plants in this study the index is based on palynological data but can be equally applied when quantitative macrofloral counts are available gi versus tpi values show two general trends of peat swamp evolution low gi and tpi values as indicator for drier swamp conditions like ombrogenous mires and high gi and tpi values which show a trend to water covered environments like topogenous mires in addition ash yields and gwi versus vi data also emphasize a general trend from topogenous to ombrogenous mires a decrease in water level towards the top of the seams and thus resulting in the development of domed mires is reflected by the newly introduced wci hence these parameters show recurrent peat swamp successions characterized by mineral and vitrinite rich coals typical for topogenous swamps and an evolution towards inertinite liptinite rich coals with low ash yield typical for ombrogenous swamps n alkane ratios like the carbon preference index cpi pristane n c17 phytane n c18 pristane phytane and the n c17 n c27 relationship indicate a strong correlation of these parameters with thermal maturity e g cpi values correlate with vitrinite reflectance sulphur organic carbon s toc ratios are quite uniform in clastic rocks with low to moderate toc contents but highly variable in coals probably reflecting variable sulphate availability during deposition of peats sphenophyll rich floral assemblages are restricted to low sulphur environments