environmental conditions for the presence of magnetofossils in the last glacial maximum inferred from magnetic parameters of sediments from the ulleung basin east sea abstract magnetic characterization of sediments from the ulleung basin in the east sea japan sea was carried out to decipher changes in environmental conditions over the last 39 000 years magnetic susceptibility intensities of natural remanent magnetization nrm anhysteretic remanent magnetization arm partial arm parm and saturation isothermal remanent magnetization sirm were measured for selected samples irm acquisition hysteresis and first order reversal curve forc measurements were made the ratios of rock magnetic parameters such as arm sirm arm and s ratio were determined to identify magnetic grain size and mineralogical variations along with electron microscope observations of magnetic mineral extracts down core variations in rock magnetic parameters for the 5 21 m long sediment core reveal distinct intervals with different grain size concentration and composition of magnetic minerals the uppermost portion and the high magnetic intensity zone hiz in marine isotope stage mis 2 are characterized by higher concentrations of fine grained magnetite whereas the mis 1 and 3 intervals contain lower concentrations of coarser grained magnetic minerals with increasing influence of hematite and or iron sulphide minerals the hiz interval is inferred to contain high occurrences of fine grained bacterial magnetosomes based on geochemical proxies east sea conditions for the hiz interval coincident with the last glacial maximum lgm can be summarized as having low total organic carbon toc enhanced eolian contributions from terrestrial organic particles and iron bearing minerals under the influence of an intensified east asian winter monsoon along with iron reducing but not sulphidic conditions that favoured growth and preservation of magnetotactic bacteria the delicate balance between reductive dissolution of magnetofossils under sulphidic conditions and production and preservation of magnetotactic bacteria in overlying iron reducing sediments for the hiz interval is responsible for the resultant abundance variations of magnetosomes in the studied sediments

swelling induced volumetric strains internal to a stressed coal associated with co2 sorption abstract it is generally accepted that typical coalbed gases methane and carbon dioxide are sorbed both adsorbed and absorbed in the coal matrix causing it to swell and resulting in local stress and strain variations in a coalbed confined under overburden pressure the swelling interactions of gases within the coal matrix and the resultant changes in the permeability sorption gas flow mechanics in the reservoir and stress state of the coal can impact a number of reservoir related factors these include effective production of coalbed methane degasification of future mining areas by drilling horizontal and vertical degasification wells injection of co2 as an enhanced coalbed methane recovery technique and concurrent co2 sequestration such information can also provide an understanding of the mechanisms behind gas outbursts in underground coal mines the spatio temporal volumetric strains in a consolidated pittsburgh seam coal sample were evaluated while both confining pressure and carbon dioxide co2 pore pressure were increased to keep a constant positive effective stress on the sample the changes internal to the sample were evaluated by maps of density and atomic number determined by dual energy x ray computed tomography x ray ct early time images as soon as co2 was introduced were also used to calculate the macroporosity in the coal sample scanning electron microscopy sem and photographic images of the polished section of the coal sample at x ray ct image location were used to identify the microlithotypes and microstructures the co2 sorption associated swelling and volumetric strains in consolidated coal under constant effective stress are heterogeneous processes depending on the lithotypes present in the time scale of the experiment vitrite showed the highest degree of swelling due to dissolution of co2 while the clay kaolinite and inertite region was compressed in response the volumetric strains associated with swelling and compression were between 15 depending on the location although the effective stress on the sample was constant it varied within the sample as a result of the internal stresses created by gas sorption related structural changes sem images and porosity calculations revealed that the kaolinite and inertite bearing layer was highly porous which enabled the fastest co2 uptake and the highest degree of compression

organic facies and palynofacies nomenclature classification and applicability for petroleum source rock evaluation abstract the basic aim of the investigation presented in this paper was to determine all relevant petrographical and geochemical characteristics of organic facies and their correlation with the lithological composition sedimentation conditions and paleoenvironments application of geological and geochemical methods gives new insight into problems concerning determination of the potential and efficiency of petroleum source rocks in making the qualitative and quantitative analyses of organic matter in this study various analytical methods were used whole rock samples kerogen concentrates transmitted and reflected normal and fluorescent light the type of organic facies was used as a criterion for the identification accumulation and transformation of the organic matter paleobotanical studies of organic facies and palynofacies were used to identify types of vegetation and draw conclusions concerning the sedimentary environment various types of organic facies and palynofacies were classified in relation to the origin of the organic matter all sedimentary organic constituents of continental huminite vitrinite inertinite cuticle wood fragments tracheids spores and pollen and marine mostly autochthonous dinocysts algae foraminifera test linings acritarchs and amorphous organic matter origin have been grouped according to different classification systems a summary of these classifications is proposed with remarks on approximate corresponding coal macerals and selected kerogen types

reconstruction of the upper gondwana palaeoclimates based on palynostratigraphy palynofacies and sedimentology of the jurassic sequences in the tabbowa basin sri lanka abstract the palynological study of the tabbowa sediments from sri lanka reveals predominant jurassic gymnospermous pollen assemblage araucariacites australis a cooksonii a fissus and callialasporites dampieri with spore murospora florida belongs to the callovian kimmeridgian age the collective palynoflora can be correlated to the classopollis araucariacites shanbeipollenites assemblage zone of africa and the murospora florida zone of the indian subcontinent and australia showing close phytogeographic relationships from the middle to late jurassic periods palynofacies and sedimentological investigations inferred oxic dysoxic conditions that prevailed when the sediments and organic matter deposited in shallow brackish water conditions in a fluvio deltaic environment

paleointensities for 10 22 ka from volcanic rocks in japan and new zealand abstract eight volcanic rocks from japan and new zealand in the age range 10 50 ka b p were studied using the thellier method paleointensity experiment and yielded five successful results for 10 22 ka samples from the shikotsu kuttara and daisen volcanoes in japan were taken from pyroclastic flows both welded and non welded and a pumice fall deposit one of the two new zealand rocks is a rhyolite lava from the taupo volcanic zone four sites out of seven located on rocks that are not usually subjected to thellier s experiment yielded successful results which indicates that volcanic products such as pyroclastic flows and rhyolite lavas are as good a material as basalt and andesite lavas for application of the paleointensity experiment one paleointensity from new zealand at 9 9 ka is very large at about 100 t and provides support for the paleointensity high found in europe and japan 1 2 the other four paleointensities for 14 22 ka are smaller than the present day value and this agrees with the idea of a broad paleointensity minimum for the period 10 50 ka that was suggested by mcelhinny and senanayake 3 it is also noted that the variation curve of absolute paleointensity from the volcanic rocks is reasonably similar to the relative paleointensity curves from marine and lake sediments which were summarized by tauxe 4

organic petrological and geochemical appraisal of the upper jurassic naokelekan formation kurdistan iraq abstract upper jurassic naokelekan formation being part of the intercepted strata of the well known miran oilfield in kurdistan region of northern iraq has been previously extensively evaluated as a potential effective source rock mainly by means of organic geochemistry in the present study a total of 60 samples were collected from four naokelekan fm outcrops those of banik galy derash barsarin and dwawa in order to conduct organic petrographical study and organic geochemical assessment including both biomarker and rock eval analyses the average recorded toc content for banik galy derash barsarin and dwawa section is considerable to very high corresponding to values of 27 5 9 0 3 5 and 5 2 wt respectively with the highest values representing the notably organic rich bottom part of the formation known as coal layer according to the petrographical analysis solid migrabitumens comprise the predominant component for all the analysed samples whereas the maceral groups of vitrinite liptinite and or inertinite showcase a minor to trace occurrence in terms of organic geochemistry each of the four sections of interest shows a different biomarker profile nevertheless a number of calculated parameters related to kerogen type and depositional conditions including the isoprenoids n alkanes ratios suggest a mixed terrestrial marine organic matter furthermore as indicated by the ro measurements along with rock eval parameters and the vitrinite reflectance equivalent based on aromatic compounds the maturity level is marginally mature in the cases of banik and galy derash whereas in the cases of dwawa and barsarin sections it is mature to post mature a synthesis of the organic petrography and geochemical appraisal applied in the present study suggests that the reported solid hydrocarbons in naokelekan fm particularly at its basal layers are non indigenous migrated and the precursor organic matter was deposited in a marine environment under oscillating conditions ranging from euxinic to well oxygenated accordingly the organic features of the notably bitumen rich coal bed fit the profile of a reservoir and or migration path

spline analysis of holocene sediment magnetic records uncertainty estimates for field modeling 1 sediment and archeomagnetic data spanning the holocene enable us to reconstruct the evolution of the geomagnetic field on time scales of centuries to millennia in global field modeling the reliability of data is taken into account by weighting according to uncertainty estimates uncertainties in sediment magnetic records arise from 1 imperfections in the paleomagnetic recording processes 2 coring and sub sampling methods 3 adopted averaging procedures and 4 uncertainties in the age depth models we take a step toward improved uncertainty estimates by performing a comprehensive statistical analysis of the available global database of holocene magnetic records smoothing spline models that capture the robust aspects of individual records are derived this involves a cross validation approach based on an absolute deviation measure of misfit to determine the smoothing parameter for each spline model together with the use of a minimum smoothing time derived from the sedimentation rate and assumed lock in depth departures from the spline models provide information concerning the random variability in each record temporal resolution analysis reveals that 50 of the records have smoothing times between 80 and 250 years we also perform comparisons among the sediment magnetic records and archeomagnetic data as well as with predictions from the global historical and archeomagnetic field models combining these approaches we arrive at individual uncertainty estimates for each sediment record these range from 2 5 to 11 2 median 5 9 interquartile range 5 4 to 7 2 for inclination 4 1 to 46 9 median 13 4 interquartile range 11 4 to 18 9 for relative declination and 0 59 to 1 32 median 0 93 interquartile range 0 86 to 1 01 for standardized relative paleointensity these values suggest that uncertainties may have been underestimated in previous studies no compelling evidence for systematic inclination shallowing is obtained from the analysis of the available database of holocene sediment magnetic records the analysis highlights the importance of collecting oriented cores publishing and archiving unprocessed raw paleosecular variation determinations and presenting a detailed chronology so that changes in the sedimentation rate can be assessed with regard to future field models workers should consider rejection of anomalous cores through comparisons to other sources and ensure that realistically large uncertainties are allocated to high latitude declination records

control and prevention of gas outbursts in coal mines riosa olloniego coalfield spain abstract underground coal mines have always had to control the presence of different gases in the mining environment among these gases methane is the most important one since it is inherent to coal despite of the technical developments in recent decades methane hazards have not yet been fully avoided this is partly due to the increasing depths of modern mines where methane emissions are higher and also to other mining related circumstances such as the increase in production rates and its consequences difficulties in controlling the increasing methane levels increasing mechanization the use of explosives and not paying close attention to methane control systems the main purposes of this paper are to establish site measurements using some critical parameters that are not part of the standard mining control methods for risk assessment and to analyze the gas behavior of subvertical coal seams in deep mines in order to prevent gas incidents from occurring the ultimate goal is the improvement in mining conditions and therefore in safety conditions for this purpose two different mines were instrumented for mine control and monitoring both mines belong to the riosa olloniego coalfield in the asturias central basin spain and the areas instrumented are mined via subhorizontal sublevels at an actual depth of around 1000 m under the overburden of mount lusorio during this research a property favoring gas outbursts was site measured for the first time in an outburst prone coal 8th coalbed gas pressure and its variations which contributed to complete the data available from previous characterizations and to set some guidelines for assessing the potential outburst prone areas a gas measurement tube set has been designed for measuring gas pressure as well as its variation over time as a result of nearby workings and to calculate permeability the paper establishes the effect of overlapping of works but it also shows the efficacy of two preventive measures to be applied high pressure water infusion and the exploitation of a protective coal seam 7th coalbed that must be mined preferably two complete sublevels before commencing the advance in the outburst prone coalbed both measures constitute an improvement in the mining sequence and therefore in safety and should be completed with a systematic measurement to control the risk gas pressure in the 8th coalbed in the area of influence of other workings to establish the most suitable moment to renew the advance further researches could focus on ascertaining the permeability not only in mined areas but also in areas of the mine that are still not affected by mining work and on tuning more finely the ranges of influence of overstress time and overlap distance of the workings of the 7th coalbed in the 8th coalbed

holocene geomagnetic secular variation records from north eastern australian lake sediments summary secular variation records have been obtained from cores from lakes barrine and eacham two north eastern australian volcanic crater lakes the results from several cores have been stratigraphically correlated and then stacked and smoothed the chronology provided by radiocarbon dating indicates that the lake eacham sequence spans the last 5700 calendar years the time scale for the lake barrine record is less weil constrained but it

a 2000 year geomagnetic field record from the gulf of papua abstract a high resolution holocene record of geomagnetic field direction and intensity in the gulf of papua was constructed using paleomagnetic data from eight piston cores collected in the region the chronology of the cores was based largely on radiocarbon dates from benthic foraminifera correlation of seismic reflectors imaged in subbottom data between nearby cores was consistent with the chronostratigraphic framework based on radiocarbon dates and provided additional confidence of the age model in other regions where cores sampled different depositional settings associated with the three dimensional prograding lobes reflectors could not be confidently correlated between cores furthermore radiocarbon ages from the bottoms of trigger cores and tops of co located piston cores revealed varying amounts of overpenetration of the piston core below the seafloor the relative paleointensity and a general eastward trend in the declination and steepening of the inclination in our new record are generally compatible with the closest 4300 km existing records our record does not agree well with global field models cals3k and pfm9k likely reflecting the lack of existing data contributing to field models in the region

jurassic tectono sedimentary evolution of the northern lusitanian basin offshore portugal abstract the lusitanian basin is one of a series of rift related basins developed during the rifting that led to the break up of iberia and canada the strong influence of halokinesis on the depositional evolution of its northern sector provides an analogue for the development of other evaporite prone rift basins on atlantic type passive margins in this paper the pre valanginian evolution of the northern lusitanian basin is documented based on regional seismic stratigraphy isochron and time structure maps tied with sonic and stratigraphic data from 10 exploration wells the pre salt structure of the study area is marked by two sets of faults i a n s to ne sw striking set active throughout the jurassic period and ii a nw se striking set active during the late jurassic the latter defines five late jurassic sub basins northeast of a basin margin structure the marinha grande fault the development of half graben basins in the northern lusitanian basin during the jurassic was overprinted by halokinesis over the marinha grande fault and other major marginal basement faults halokinesis climaxed during the oxfordian kimmeridgian rifting with the formation of a 10 km long salt ridge over the marinha grande fault the ridge limited the southward progradation of fluvial deltaic units derived from hanging wall drainage systems and restricted the syn rift sediments to a 15 km long 5 km wide bowl shaped depocentre located 10 km west of the present coastline in order to better characterise the jurassic tectono sedimentary evolution of the northern lusitanian basin the interpreted seismic data is compared with physical models for extensional forced folds above active normal faults and with stratigraphic information from well and outcrop

solid bitumen bituminite and thermal maturity of the upper jurassic lower cretaceous chia gara formation kirkuk oil field zagros fold belt kurdistan iraq abstract the upper jurassic lower cretaceous chia gara formation a proven marine source rock characterised by predominance of amorphous organic matter aom is known from few outcrops in ne iraq and a number of exploration wells in the zagros fold belt this study presents comprehensive organic petrographic and mineralogical investigations of the dispersed organic matter and rock forming minerals of the tithonian berriasian chia gara formation intersected by the kirkuk well k 109 drilled in the giant kirkuk oil field ne iraq the organic petrographic analyses including incident light microscopy and confocal laser scanning microscopy clsm were applied to carbonate source rocks with low to moderate organic carbon contents our data demonstrate the predominance of bituminite and solid bitumen among the examined dispersed organic matter followed by oil exudates and oil globule inclusions as well as the presence of minor contributions of alginite i e tasmanites and leiospheridia liptodetrinite and vitrinite based on optical characteristics and clsm spectral fluorescence measurements examinations of bituminite point towards the presence of bituminite type iii the bituminite type iii encloses dark orange fluorescent amorphous components suggesting a genetic relationship either with liptodetrinite and or with solid bitumen the qualitative assessment of solid bitumen reveals several dissimilar forms identified in the analysed samples the photometric and spectral fluorescence measurements point to distinct reflectance values ranging between 0 19 and 0 43 sbrr and lambda max values extending from 515 nm to 590 nm respectively the corresponding results of the solid bitumen exhibit 1 a lack of a relationship with depth and 2 suggest its poor property as a reliable maturity indicator for the examined samples the presence of oil exudates oil globule inclusions and their association with solid bitumen suggests a genetic relation with the examined residues of liquid hydrocarbon phase the performed thermal maturities assessments of dispersed organic matter point towards early mature to peak mature oil window with vitrinite reflectance values ranging between 0 52 vrr at 2801 m to 0 83 vrr at 3089 m depth mineralogical analyses revealed the predominance of calcite over dolomite in the examined limestone to marl lithofacies e g clear rimmed dolomite with localised intensive dolomitisation in the phyllosilicate rich matrix predominance of calcite and siderite is observed followed by zinc blende and pyrite the composition of organic matter in the examined chia gara formation with predominance of bituminite and solid bitumen makes the major marine source rock of iraq s cretaceous petroleum systems distinctive in terms of hydrocarbon generation and migration at an oil window stage as it provides suitable explanations for its generally low hydrogen index hi with only minor terrestrial input in addition the results presented herein can be helpful for future evaluation of thermal maturities and characterisation of optical appearances of dispersed organic matter in carbonates by incident light microscopy and especially by clsm during hydrocarbon prospecting

paleomagnetic secular variation records from holocene sediments of lake victoria 0 5 s 33 3 e we have conducted a paleomagnetic study of holocene sediments from lake victoria in order to develop a high resolution record of paleomagnetic secular variation psv this study has recovered psv

biomarkers as environmental indicators in a carbonate complex example from the middle to upper devonian holy cross mountains poland abstract autochthonous biomarker distributions were studied in an array of different subfacies of a devonian carbonate complex represented in platform reef and off platform shelf basinal systems it revealed that biomarkers are sensitive indicators of depositional environments and may serve to refine palaeoenvironmental interpretations of carbonate complexes based on classical sedimentological facies analyses the contrasting biomarker composition of the carbonate platform and reef complex versus shelf basin deposits is here interpreted as the effect of both more diverse biotic sources of a primary organic matter in the former environments highly scattered results of sterane distribution and contrasting styles of decay and bacterial reworking of the primary biomass peritidal dolostones deposited under anoxic to suboxic conditions and with scarce sedimentological evidence of elevated salinity reveal the highest potential of organic matter preservation among other platform reefal facies their biomarker composition includes several compounds indicating hypersaline conditions and anoxia whereas others in particular gammacerane indicate that the water column was stratified during sedimentation this observation constrains environmental interpretation of these deposits pointing to shallow subtidal lagoons with elevated salinity and low oxygen near bottom waters most probably originating from a salinity controlled stratification of the water column biomarkers diagnostic of green sulphur bacteria were found in both peritidal lagoonal dolostones and shelf basinal facies this indicates the existence of photic zone anoxia in the latter environment thus suggesting a shallow position of the redoxcline the frasnian famennian mass extinction event s apparently had no impact on the biomarker distribution in the shelf basinal system continuous across the stage boundary

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

holocene break up and reestablishment of the petermann ice tongue northwest greenland abstract over the last decade two major calving events of the petermann ice tongue in northwest greenland have led to speculation on its future stability and contribution to further greenland ice sheet mass loss however it has been unclear if these events are anomalous or typical within the context of limited historical observations we extend the historical record of the floating ice tongue using the stratigraphy of petermann fjord sediments to provide a longer term perspective computed tomography ct scans x ray fluorescence xrf scans ice rafted debris ird counts and the magnetic properties of specific particle size fractions constrain changes in depositional processes and sediment sources at our core sites allowing for reconstructions of past behavior of the petermann ice tongue radiocarbon dating of foraminifera 210pb and paleomagnetic secular variation psv provide age control and help to address uncertainties in radiocarbon reservoir ages a floating ice tongue in petermann fjord formed in late glacial time as petermann glacier retreated from an advanced grounded position this paleo ice tongue broke up during the early holocene when high northern latitude summer insolation was higher than present after gradual regrowth of the ice tongue associated with regional cooling the ice tongue reached its historical extent only within the last millennium little or no ice tongue was present for nearly 5000 years during the middle holocene when decadal mean regional temperatures are estimated to be 0 8 2 9 c higher than preindustrial 1750 ce and seasonal sea ice in the lincoln sea was reduced this pre historical behavior shows that recent anthropogenic warming may already be in the range of ice tongue instability and future projected warming increases the risk of ice tongue break up by the mid 21st century

relative paleointensity of the earth s magnetic field from marine sedimentary records a global perspective abstract to assess the potential of marine sediments as a source of relative paleointensity information we have undertaken an investigation of selected box cores stored in the scripps core repository we present here new results from two north atlantic box cores magnetic remanence in the sediments is carried by magnetite and is univectorial during alternating field and thermal demagnetization the median destructive field is 25 30 mt normalization by anhysteretic remanent magnetization yields relative paleointensity data that are highly concordant within and between cores age control provided by oxygen isotope data from both cores allows comparison of these relative paleointensity data with contemporaneous archeomagnetic data from czechoslavakia both data sets indicate a peak in paleofield intensity at around 8 10 ka this peak is less prominent in box core data from the western pacific and global averages of archeomagnetic and lava flow data however the peak is evident in data estimating changes in production of radiocarbon which is controlled in part by changes in the dipole moment of the geomagnetic field the excellent agreement between production variations predicted by the changes in dipole moment and those observed suggests that long term variations in atmospheric radiocarbon are dominated by geomagnetic field variations

palaeointensity in the pelagic realm marine sediment data compared with archaeomagnetic and lake sediment records summary four box cores collected from the ontong java plateau during the eurydice expedition have been used to make relative geomagnetic palaeointensity measurements rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy and that they are suitable for relative intensity estimates these are obtained by normalizing the nrm by an arm imparted in a low dc bias field the palaeoceanographic event known as the preservation spike is used to establish a crude time scale for the record so that it may be compared with other data from the same region and also with global palaeointensity estimates the marine sediment data are quite similar to australian intensity data from lake sediments and archaeomagnetic sources but as might be expected exhibit some obvious differences from the global record

holocene climatic evolution at the chinese loess plateau testing sensitivity to the global warming cooling events abstract a high resolution petromagnetic analysis demonstrates that pedogenic alterations in holocene loess sand sequences from the regions of the guanzhong basin and the mu us desert on the chinese loess plateau clp were affected by climatic variations in temperature and precipitation three warm humid intervals 8 4 3 7 2 4 1 2 and 0 81 0 48 ka associated with soil formation and relatively high values of petromagnetic parameters occurred during the holocene a substantial paleosol development from 8 4 to 3 7 ka and higher petromagnetic parameter values indicate a generally strong warm humid phase in the mid holocene which can be attributed to the holocene climatic optimum our study demonstrates that the holocene climate in the eastern part of the clp is sensitive to warming and cooling events linked to global changes in temperature and precipitation a complete holocene climate record is constructed correlating well with the other regional climate records along the south to north profile on eastern clp and suggesting that similar climatic changes occurred in eastern monsoonal china during the holocene results are supported by other climate records in different regions of the world and imply that the holocene climatic optimum in the northern hemisphere probably took place at the same time

lithology sedimentology and genesis of the wadena drumlin field minnesota u s a abstract studies on both the regional and small scales of the lithology sedimentology and stratigraphy of the wadena drumlin field in central minnesota u s a provide insights to the processes that operated within the wadena lobe during the drumlin forming phase horizontal changes in the down glacier direction in the nature of the drumlin till include an increase in the carbonate content decrease in grain size and magnetite content and variations in fine fraction mineralogy these changes also occur with depth at individual sites it is inferred that these patterns reflect progressive incorporation and mixing of the substrate which for much of the drumlin field is a till of northwestern origin with the till already in transit within the base of the wadena lobe derived from the northeast factors contributing to enhanced erosion within the wadena drumlin field include increased vertical strain rates over a major subglacial highland the presence of deformable bed material and a lowered ice profile which permitted elevated rates of bed deformation the patterns of mixing are generally consistent with substrate incorporation either by regelation or in the context of a deforming bed although neither of these processes adequately explain all of the observed features of the drumlin till where localized departures from the generalized pattern exist it can be shown that these are the result of either syn or post depositional processes primarily winnowing or the influence of a different substrate additional data are presented including macrofabric measurements and detailed site descriptions that are consistent with an accretionary progressive build up of the drumlin forms

paleoenvironmental characterization of a jurassic sequence on the bombarral sub basin lusitanian basin portugal insights from palynofacies and organic geochemistry abstract a middle upper jurassic sedimentary succession has been cut by the ramalhal 1 borehole in the bombarral sub basin lusitanian basin portugal the succession comprises the brenha montejunto abadia and lourinha formations which are composed of limestones marls sandstones and clays the main objective of this study was to characterize the organic matter using palynofacies and geochemical analyses to determine the depositional paleoenvironments and the hydrocarbon generation potential the total organic carbon content is generally less than 1 wt but reaches 4 1 wt in one sample due to the presence of perhydrous coal the rock eval pyrolysis results reveal lower values hi usually nether to 100 mghc gtoc showing that the studied samples have type iii kerogen and a low potential for oil generation the t max values varies between 319 and 443 c and biomarker data obtained for these samples indicate a maturation ranging between immature and eventually mature the palynofacies data indicate predominance of the phytoclast group 80 with different degradation degrees and a modest contribution of palynomorph group especially sporomorphs and the amorphous organic matter aom group solid bitumen was observed in some samples from the montejunto and brenha formations determining the relative percentages of the kerogen groups allowed for the identification of seven intervals that established variations in the depositional environment

reconstructing holocene geomagnetic field variation new methods models and implications reconstructions of the holocene geomagnetic field and how it varies on millennial timescales are important for understanding processes in the core but may also be used to study long term solar terrestrial relationships and as relative dating tools for geological and archaeological archives here we present a new family of spherical harmonic geomagnetic field models spanning the past 9000 yr based on magnetic field directions and intensity stored in archaeological artefacts igneous rocks and sediment records a new modelling strategy introduces alternative data treatments with a focus on extracting more information from sedimentary data to reduce the influence of a few individual records all sedimentary data are resampled in 50 yr bins which also means that more weight is given to archaeomagnetic data during the inversion the sedimentary declination data are treated as relative values and adjusted iteratively based on prior information finally an alternative way of treating the sediment data chronologies has enabled us to both assess the likely range of age uncertainties often up to and possibly exceeding 500 yr and adjust the timescale of each record based on comparisons with predictions from a preliminary model as a result of the data adjustments power has been shifted from quadrupole and octupole to higher degrees compared with previous holocene geomagnetic field models we find evidence for dominantly westward drift of northern high latitude high intensity flux patches at the core mantle boundary for the last 4000 yr the new models also show intermittent occurrence of reversed flux at the edge of or inside the inner core tangent cylinder possibly originating from the equator less

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

the structural and sedimentary evolution of the arruda and lower tagus sub basins portugal abstract the study discusses the jurassic structural and sedimentary evolution of the arruda and lower tagus sub basins located in the central and southern part of the lusitanian basin of portugal in the last five decades thousands of kilometres of 2d seismic reflection lines were acquired for oil exploration reprocessing and reinterpretation of over 700 km from the study area was carried out after the seismic to well ties based on well logs vsp analysis synthetic seismograms revised petrological analysis and stratigraphic reinterpretation of the wells nine key seismic geologic horizons were mapped and depth converted reinterpretation of the seismic profiles was carried out using outcrop data and reprocessed aeromagnetic and gravimetric data of the study area that was integrated in a gis environment several aspects of the tectonic and sedimentary evolution of the study area were enlightened from the triassic until the late jurassic two rift phases were recognised in agreement with data from other parts of the lusitanian basin the initial rifting phase in the triassic continued until the callovian with three prominent tectonic pulses a first in the late triassic a second in the hettangian and a third from the sinemurian onwards the latter episode lasted until the callovian in the arruda sub basin and at least until the bathonian in the lower tagus sub basin during the middle jurassic the arruda sub basin evolved to a nw deepening carbonate ramp the lower tagus sub basin constituted a platform since the early jurassic limited in the east by the setubal pinhal novo fault and in the west by the cadafais fault the third rifting episode occurred in the late oxfordian early kimmeridgian producing a major n s fault system already recognised by several authors and another important nw se and ne sw fault systems post dating the former

magnetic mineral tracing of sediment provenance in the central bengal fan abstract we present a comprehensive magnetic mineral analysis of surface sediments from 110 sites in the central bengal fan to trace sediment provenance multiple magnetic parameters including magnetic mineralogy concentration and grain size were generated rock magnetic measurements indicate that the dominant magnetic minerals within the studied sediments are detrital magnetite and titanomagnetite which is further confirmed directly by scanning electron microscope sem and transmission electron microscope tem observations on magnetic extracts fuzzy c means clustering analysis of magnetic parameters indicates that the study area can be divided into three clusters considering the position of active valley we further divide cluster 1 into clusters 1a and 1b cluster 1a primarily covers the west side of the active valley with relatively high magnetic concentrations and dominantly coarse grained magnetic minerals which likely correspond to basaltic materials derived from the deccan plateau from the godavari river mouth to the inner bay of bengal magnetic concentration gradually decreases with a fining trend of magnetic grain size clusters 1b 2 and 3 are on the east side of the active valley where magnetic concentration and magnetic grain size decrease with increasing distance to the active valley combined with published data in the indian region and the upper bengal fan we suggest that the main provenances are the himalayan and the deccan plateau whose contributions to sediment distribution are quantitatively assessed our analysis suggests that the position of active valley plays a key role in sediment distribution in the central bengal fan while the effect of ocean currents is negligible

on the use of calibrated relative paleointensity records to improve millennial scale geomagnetic field models current millennial scale time varying global geomagnetic field models suffer from a lack of intensity data compared to directional data because only thermoremanently magnetized material can provide absolute information about the past field strength the number of archeomagnetic artifacts that can provide such data diminishes rapidly prior to 3000 b c sediment cores provide time series of declination and inclination and of variations of magnetization the latter can reflect relative geomagnetic field variations if suitably normalized we propose a calibration technique based on predictions from global models and use the cals7k 2 model to calibrate relative paleointensity records from 22 globally distributed locations and assess whether they reflect actual field variations all except a few contain useful information for 0 to 7 ka and could be used to improve the existing models using synthetic data from a numerical dynamo simulation we show that with the existing directional data the distribution of intensity data has an important influence on model quality intensity data from a broad range of latitudes seem particularly important this study opens the possibility of extending global time varying geomagnetic field models further back in time than the current 7 kyr interval

organic matter deposition and paleoenvironmental implications across the cenomanian turonian boundary of the subalpine basin se france local and global controls abstract the cenomanian turonian boundary is marked by global sea level highstands and one of the warmest periods of the mesozoic with high pco2 levels linked to a massive magmatic episode this is associated with the establishment of a worldwide marine anoxia the deposition of organic rich facies and disturbances of the global carbon cycle the so called oceanic anoxic event 2 oae2 the pont d issole section s subalpine basin se france sedimentary succession represents the reference record of oae2 in the tethyan domain although its organic fraction is extremely poorly studied therefore the main objectives of this study are the characterization of the pont d issole section s organic matter om for paleoenvironmental interpretation and the assessment of the om thermal maturity using organic petrology and organic geochemistry techniques the organic record characterizes a shallowing up marine system with varying redox and restriction conditions associated with periods of stratified oxygen regimen it displays the presence of two om enrichment episodes with different paleoenvironmental and geodynamic contexts the first om enrichment episode unit th1 is thought to be associated with the global mechanisms that trigger oae2 and is characterized by a palynofacies association co dominated by amorphous om and marine microplankton reflecting a context of high sea level this is followed by the plenus cold event unit th2 characterized by a decrease in amorphous om and increase in marine microplankton representing a reoxygenation associated with an increase in water level and an apparent decrease in temperature disappearance of classopollis sp the second om enrichment episode unit th3 and base of unit th4 is characterized by an association dominated by amorphous om the occurrence of freshwater microplankton and the development of a restricted environment with low sea level these depositional conditions are thought to be connected to the beginning phases of basin closure promoted by the regional tectonic framework compressive trend between africa and europe the molecular fraction showed the presence of unsaturated compounds monoaromatic steranes monoaromatic anthrasteroids and the biological hopanes indicating a low thermal evolution for the om this is corroborated by biomarkers ratios and organic petrographic data namely vitrinite reflectance 0 29 rr the presence of paleozoic reworked om in the samples was also identified presenting a more complex thermal history than the cretaceous om this om is possibly related to the subaerial erosion of hercynian massifs

the mesozoic cenozoic organic facies in the lower tagus sub basin lusitanian basin portugal palynofacies and organic geochemistry approaches abstract studies of the mesozoic and cenozoic sequence crossed by the barreiro 4 borehole provide an improved understanding of the organic matter deposited in the lower tagus sub basin lusitanian basin portugal and the implications for the potential source rock and depositional environment this study focused on 43 samples middle jurassic to neogene that were subjected to palynofacies and organic geochemistry analyses total organic carbon rock eval pyrolysis and molecular biomarker analysis the palynofacies data indicate that the sequence contains mainly phytoclasts non opaque phytoclasts however the middle jurassic samples are dominated by amorphous organic matter aom continental and or marine palynomorphs are present in all the samples the cretaceous samples are characterized by small amounts of kerogen that have high contents of solid bitumen the total organic carbon toc content is generally less than 1 wt the rock eval s1 and s2 parameters vary from 0 01 to 3 50 mghc g rock and 0 15 to 34 03 mghc g rock respectively with the highest values corresponding to the cretaceous samples the hydrogen index hi and oxygen index oi values range from 35 to 552 mghc g toc and 4 to 180 mghc g toc respectively the tmax values range from 416 to 437 c the biomarker analysis showed that n alkanes with 15 30 carbon atoms are present and usually have a unimodal distribution with a predominance of low to medium molecular weight compounds the cpi values range between 0 63 and 3 65 and the pristane phytane ratios vary between 0 48 and 1 64 indicating alternation of oxic anoxic conditions along the sequence the distribution of terpanes shows small amounts of tricyclic and tetracyclic terpanes in most of the samples except for some cretaceous samples and a predominance of pentacyclic terpanes the amount of 17 h 22 29 30 trisnorhopane tm usually exceeds the amount of 18 h 22 29 30 trinorneohopane ts the 20s 20s 20r and ratios of the c29 steranes generally have values below the range of equilibrium indicating an immature stage of the om

gas emission prediction and recovery in underground coal mines abstract strata gas can be released and captured from non active and active gas resources either from virgin or relaxed strata both prior to and when mining activities take place the high and irregular gas emissions associated with high production longwall mining have provided a need to optimise the methods used to predict these gas levels and the ventilation requirements for gas dilution a forecast of gas emissions during development drivage and longwall mining indicated possible gas and ventilation problems requiring the introduction of various gas drainage techniques and in maintaining the necessary air quantities in ventilation systems to satisfy the statutory gas limitations for various coal production rates although there are sound principles used in world recognised methods of gas emission prediction a new approach developed from long term practical experience in underground gassy coal mine practices and gas rock mechanics studies appear most suitable for local conditions and mining systems in use the lunagas floorgas and roofgas geomechanical and gas emission models offer an effective solution to these problems both programs are the most advanced engineering numerical tools available to calculate gas source contributions to total gassiness and improve the accuracy and quality of gas control gas capture technologies and ventilation system design

evaluating late holocene radiocarbon based chronologies by matching palaeomagnetic secular variations to geomagnetic field models an example from lake kalimpaa sulawesi indonesia palaeomagnetic and palaeoenvironmental data from indonesia and particularly from the island of sulawesi are scarce and exact dating has turned out to be a challenge in many archives from this region here we outline difficulties in radiocarbon dating of the palaeoenvironmental record from lake kalimpaa sulawesi indonesia these difficulties demand the integration of additional parameters to obtain a reliable chronology for this record thus we compare the palaeo magnetic secular variation data from this record with the cals3k 4 spherical harmonic geomag netic model of the 0 3 ka field korte constable 2011 the resulting age depth model for the lake kalimpaa sequence provides a profound basis for further multi proxy investigations on this record for the first time high resolution palaeomagnetic secular variation data continuously span ning the past 1300 years are presented for this region which complement existing records with lower temporal resolution or records missing the top most sections

towards absolute calibration of sedimentary paleointensity records abstract using relative paleointensity estimates derived from twelve globally distributed pelagic sediment cores we assess whether they record a signal consistent with that expected from a dominant geocentric axial dipole the cores span the matuyama brunhes boundary and we normalize the observations by supposing that at the time the direction reverses the intensity low reflects only the non axial dipole contribution to the field we further assume that this non axial dipole contribution to the field is invariant with geographic location from absolute paleointensity compilations we estimate its size to be about 7 5 t this supplies the calibration for the axial dipole signal away from the extreme low in intensity the data predict the dipole field variation with latitude with similar accuracy to that observed in absolute paleointensity records and show similar behavior when transformed to virtual axial dipole moments

eastern australian geomagnetic field intensity over the past 14000 yr summary two north eastern australian volcanic crater lake cores have been used to obtain relative intensity estimates for the geomagnetic field arm imparted in a low dc bias field has been used as a normalizing parameter the intensity fluctuations in the two lakes are in excellent agreement with each other and with south eastern australian archaeointensity data over their coeval time spans this strongly suggests that the same sources are influencing the geomagnetic secular variation throughout eastern australia at this time the relative intensity records go back to about 14000yr bp thereby extending currently available recent australian intensity records by some 7000 yr

an environmental magnetic fingerprint of periglacial loess records of late pleistocene loess palaeosol sequences from eastern germany a detailed rock magnetic analysis of the last glacial interglacial loess palaeosol sequences was carried out in the framework of a comprehensive stratigraphic study of loess in saxony eastern germany magnetic susceptibility and laboratory induced remanences have been determined to compare individual sections and to identify the specific rock magnetic characteristics of the saxonian loess province according to the model of pedogenic magnetic enhancement an increasing neoformation of ferrimagnetic minerals in the course of pedogenesis was observed only in the uppermost late weichselian lithological units consisting of pure aeolian loess and indicating dryer climatic conditions in contrast the rock magnetic characteristics of the lower middle and early weichselian units exhibit a significant destruction of primary magnetic minerals caused by such secondary processes as climatically controlled waterlogging and reworking this change in magnetic composition with stratigraphic depth was additionally proved by factor analysis in which the main observation an increasing fd with decreasing argues for a general magnetic depletion in conjunction with decreasing magnetic grain sizes caused by weathering of larger primary particles the magnetic fingerprint of the saxonian loess is characterised by prevailing magnetic depletion processes which effectively rules out the application of the wind vigour model moreover the magnetic characteristics differ significantly from that of other loess regions and support a new and independent model which explains the magnetic behaviour of strongly reworked and waterlogged gleyed loess palaeosol sequences in the relatively humid central european periglacial areas

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

establishing a first archaeointensity record for the sw pacific abstract the dearth of archaeomagnetic intensity data from the southern hemisphere is a limiting factor in evaluating models of global geomagnetic field evolution during the holocene here we present high quality microwave archaeointensity data obtained from 34 ceramic fragments 21 archaeological contexts from the duke of york islands fiji and vanuatu sw pacific complementary thellier type experiments corrected for anisotropy give good agreement with the microwave results the majority of the new data prior to 250 ad exhibit significantly lower intensity than predicted by current global field models cals3k 3 and arch3k for the region with an apparent intensity minimum at 250 bc reaching as low as 50 of the present day field strength between 400 ad and 1500 ad the data are broadly consistent with the global field models but with a 20 higher field between 1200 and 1400 ad these new results therefore imply that the geomagnetic field has a greater range of variability than predicted and that further data from the region are essential to better constrain the global field models the results also demonstrate that establishing an archaeomagnetic reference curve for dating sw pacific ceramic artefacts is feasible which has potentially significant implications for pacific archaeological research

normalized remanence in sediments of the western equatorial pacific relative paleointensity of the geomagnetic field piston cores from the ontong java plateau collected during the eurydice expedition have been used to estimate regional geomagnetic paleointensity rock magnetic measurements of the sediments show that 1 the remanence is carried by stable pseudo single domain magnetite 2 the grain sizes and concentrations are relatively uniform with respect to the normalization technique and 3 susceptibility is an adequate parameter for normalizing remanent intensity in order to determine relative variations in the intensity of the paleomagnetic field we therefore have measured the remanent intensity both natural and demagnetized to 15 mt and susceptibility of archive quarters of three cores at centimeter intervals using an automated through bore magnetometer a further test of the normalized intensity records is provided by the coherence function between the normalized remanence and the susceptibility of the cores one of our cores displays high coherence over a broad range of frequencies while for two others coherence is insignificantly different from zero at the 95 level of confidence oxygen isotopic records paleontological datum levels and the brunhes matuyama boundary provide an independent temporal framework for inter core comparison when the two cores which pass our acceptance criteria are placed on a common time scale the coherence between the normalized intensity records is significantly different from zero at well above the 95 level of confidence suggesting some common input signal over the same band of frequencies furthermore there is a great deal of similarity between the records from the ontong java plateau and a record from core rc10 167 taken some 3000 km to the north the distribution of intensities obtained from these sedimentary records has the same shape as the absolute virtual dipole moment data obtained from lava flows 0 5 ma with a slightly smaller standard deviation the inter core agreement within a single region the similarity of records from 3000 km apart and the general correspondence of statistical character of these sediments with lava flow data all argue that the normalized intensity records presented here reflect variations in the intensity of the ancient geomagnetic field spectral analysis of the paleointensity time series shows that there a is significant enhancement of variance concentrated in frequencies around 33 thousand years over the period 0 350 ka this feature is however lacking for the period 350 700 ka

paleointensity of the geomagnetic field during the last 80 000 years high resolution records of the relative paleointensity of the geomagnetic field have been obtained from five marine cores three duplicate records were used to estimate the regional coherency of the data within a single area tyrrhrenian sea while the two others document the field variations in the eastern mediterranean and the southern indian ocean careful investigations of distinct rock magnetic parameters have established the downcore uniformity of the sediments in terms of magnetic mineralogy and grain sizes the time depth control was provided by oxygen isotopes and small scale variations in the deposition rates were constrained by means of tephrachronology the synthetic curve calculated from the mediterranean records provides a continuous record of the intensity variations during the last 80 000 years 80 kyr which correlates well with the sparse volcanic data available for the period 0 40 kyr the fact that identical behavior is seen in both data sets and that they also compare quite well with results from a core collected in the pacific ocean establishes the truly dipolar character of these variations the dipole field moment is characterized by large scale changes as shown by the existence of pronounced drops at 39 and 60 kyr alternating with periods of higher intensity the record suggests a periodic nature for these intensity variations however the period studied is not sufficiently long to state this conclusively these results demonstrate the potential of sediments for such studies and constitute a first step towards obtaining a global paleointensity record over a long period of time

testing whether early diagenesis of skeletal carbonate is different in non marine settings contrasting styles of molluscan preservation in the upper jurassic of portugal abstract this study tests the hypothesis that the early diagenesis of aragonite shells should differ fundamentally between marine and freshwater environments this is predicted to be the case because aragonite is highly susceptible to dissolution in the taz taphonomically active zone in low energy marine settings due to acidity caused largely by the oxidation of h2s generated by sulphate reducing bacteria but reduced sulphide activity in freshwater settings should result in less early dissolution of aragonite to test this hypothesis a range of fresh brackish hypersaline and marine limestones were sampled from the upper jurassic mid oxfordian cabacos formation of central western portugal in these freshwater and brackish deposits molluscs are preserved mostly as sparite shell replacements indicating that the original aragonite was preserved through the taz and was later replaced during subsequent burial by calcite cement in limestones deposited in more marine to hypersaline settings molluscan remains mostly consist of the calcitic layers of bimineralic bivalves as shell where the original was wholly calcitic or as gastropod steinkerns exceptions occur and reflect other factors such as higher energy conditions during deposition whereby organic matter as the drive for microbial decay processes was removed the implications for molluscan preservation including some hydrocarbon reservoirs are discussed

record of a mid pleistocene depositional anomaly in west antarctic continental margin sediments an indicator for ice sheet collapse abstract modern global warming is likely to cause future melting of earth s polar ice sheets that may result in dramatic sea level rise a possible collapse of the west antarctic ice sheet wais alone which is considered highly vulnerable as it is mainly based below sea level may raise global sea level by up to 5 6 m despite the importance of the wais for changes in global sea level its response to the glacial interglacial cycles of the quaternary is poorly constrained moreover the geological evidence for the disintegration of the wais at some time within the last ca 750 kyr possibly during marine isotope stage mis 11 424 374 ka is ambiguous here we present physical properties palaeomagnetic geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the west antarctic continental margin in the amundsen sea and spans more than the last 1 myr within the sedimentary sequence proxies for biological productivity such as biogenic opal and the barium aluminum ratio and the supply of lithogenic detritus from the west antarctic hinterland such as ice rafted debris and clay minerals exhibit cyclic fluctuations in accordance with the glacial interglacial cycles of the quaternary a prominent depositional anomaly spans mis 15 mis 13 621 478 ka the proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single prolonged interglacial period even though no proxy suggests environmental conditions much different from today we conclude that if the wais collapsed during the last 800 kyr then mis 15 mis 13 was the most likely time period apparently the duration rather than the strength of interglacial conditions was the crucial factor for the wais drawdown a comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout mis 15 mis 13 some of these anomalies are observed in the pelagic southern ocean and the south atlantic and might originate in major ice sheet drawdown in antarctica but further research is required to test this hypothesis

a preliminary magnetic study of soil samples from west central minnesota abstract various rock magnetic techniques were applied to characterize magnetically the samples of a soil profile taken from west central minnesota there is a marked change in magnetic properties as a function of depth in the core x ray analysis and curie temperature measurements carried out on the magnetic fractions indicate that magnetite is the dominant iron oxide in both the top soil and the subsoil the intensity of anhysteretic remanent magnetization arm decreases sharply as the depth increases in contrast the stability of arm was found to be higher for the subsoil the surface soil sample was capable of acquiring a significant amount of viscous remanent magnetization vrm the vrm acquisition coefficient s a of the subsoil s a 3 18 10 6 emu g 1 3 18 10 6 a m 2 kg 1 was about ten times weaker than that of the top soil sample s a 3 868 10 7emu g 1 3 868 10 7 a m 2 kg 1 the magnetic domain state indicator the ratio of coercivity of remanence to coercive force h cr h c was 1 5 and 3 85 for the top soil and subsoil respectively it appears that the observed variations in magnetic properties down the present soil core is due only to a difference in grain size we conclude that the magnetic grains in surface soil samples were more single domain sd like whereas the magnetite grains in the subsoil samples were more likely in pseudo single domain psd or small multidomain md range the observed lower stability for the surface soil samples is attributed to the presence of superparamagnetic grains whose presence was confirmed by transmission electron micrographs

relative variations in geomagnetic intensity from sedimentary records the past 200 000 years abstract eighteen records of relative paleointensity from marine sediments have been compiled in order to retrace the global changes in geomagnetic intensity during the past 200 kyr before dealing with any other source of noise we focused on problems inherent to the depth versus time correlations the accuracy and resolution of dating mostly deduced from isotopic stratigraphy were identified as significant factors of distortion we found also that different time scales have been used by authors after readjustment with respect to the same time scale the records were stacked together and the statistical significance of the results tested by a bootstrap technique seventeen records shown to be coherent were combined into a synthetic curve defined as sint 200 other stacks combining various subsets of data were found to be identical to sint 200 except for changes in dispersion in fact the dispersion around sint 200 could be reduced further by improving the correlations without violating the stratigraphy a procedure which at least for some records emphasizes the need for more detailed depth time correlations another characteristic emerging from the results is that paleointensity features as short as 10 kyr are observed between 120 200 ka and can thus in principle be resolved however subsequent refinement is still necessary for this period which is documented by fewer records than the following 120 kyr finally we compared sint 200 with the records from the labrador sea and the lac du bouchet ldb both of which rely mostly on 14c chronology the two records show satisfactory agreement with sint 200 when transferred with respect to the age model established by correlating their 18o labrador and susceptibility features ldb with the 18o reference record the offset of 7 kyr at 40 ka measured in both cases between the 14c and 18o ages is higher than the value deduced from a recent model of a geomagnetic field control of 14c production 1 but is not inconsistent with recent u th dates

carbonate reservoir outcrop analogues with a glance at pore scale middle jurassic lusitanian basin portugal abstract the middle jurassic carbonate successions from the lusitanian basin portugal show a range of facies deposited across a ramp depositional system well exposed over large areas these facies are valuable for understanding reservoirs and related seal and trap configurations namely in carbonate ramps this paper documents primarily shallow water units corresponding to the dominant reservoir type facies highlighting their potential as analogues particularly at outcrop but integrating main macro and micro scale characteristics the mid and inner ramp sediments which include the key studied units consist of peloidal intraclastic bioturbated fossiliferous limestones oolitic skeletal and coral algal limestones assigned to shoals and barrier island complex fossiliferous oncoidal fenestral deposits from lagoonal peritidal and locally pedogenic settings dolostones and dolomitic limestones facies with higher potential reservoir features are addressed in more detail in three broad groups sandbodies biostromes dolostones dolomitic limestones the remaining facies are more briefly described the most widespread reservoir lithofacies are cross stratified or massive oolitic and bioclastic grainstones to rudstones and coral dominated biostromes the larger scale sandbody units show a dominant sheet like geometry but wedges and smaller scale lensoid units occur grading into and interfingering with other facies types the reservoir facies are closely associated with hence often encased by flow baffle or barrier seal facies either landwards lagoonal peritidal or seawards mid outer ramp this architecture coupled with varied diagenetic paragenesis created a range of stratigraphic and diagenetic traps that may be perceived as play similarities in potential exploration situations the present reservoir quality is mostly low to moderate but examples of high excellent porosities and locally enhanced permeabilities occur overall these units are highly suitable field analogues to clarify processes leading to depositional diagenetic fractured and hybrid reservoir types moreover they clearly indicate how shoreface dynamics shallow water carbonate factory productivity and diagenesis lead to more complex reservoirs than usually appreciated in mostly homoclinal depositional systems

palynofacies and source rock potential of jurassic sequences on the arruda sub basin lusitanian basin portugal abstract the study of the organic matter present in sedimentary rocks is fundamental for the characterization of the potential source rocks as well as to define the depositional paleoenvironments parameters of organic petrology and organic geochemistry and their variations along sedimentary successions are essential tools to achieve these goals two borehole successions freixial 1 and benfeito 1 from arruda sub basin lusitanian basin that comprise siliciclastic carbonate deposits of jurassic age have been studied in order to characterize the organic matter and its vertical variability as well as its hydrocarbon potential palynofacies and geochemical data indicate both marine including zooclasts and terrestrial organic matter where the phytoclasts predominated despite an important contribution of the amorphous organic matter aom different types of solid bitumen were observed most of the analyzed samples have total organic carbon content toc lower than 1 wt and hydrogen index hi values lower than 100 mghc g toc revealing types iii and iv kerogen however one set of samples exhibit toc values higher than 1 wt and higher hi values depicting a type ii kerogen the biomarker data showed a dominance of n alkanes with 15 30 carbon atoms having a unimodal distribution pristane phytane ratio varies between 0 04 and 1 84 indicating an alternation of oxic anoxic conditions along the sequences typical terpane distributions are characterized by the presence of tricyclic and tetracyclic terpanes as well as pentacyclic terpanes rare in carbonated samples from freixial 1 borehole the amount of 17 h 22 29 30 trisnorhopane tm usually exceeds the amount of 18 h 22 29 30 trinorneohopane ts the values of the ratio 22s 22s 22r epimers of c32 homohopanes revealed that most samples reached equilibrium values the 20s 20s 20r and isomerization ratios in c29 sterane calculated for the studied samples range between 0 19 0 61 and 0 20 0 70 respectively with several samples reaching the equilibrium values the vitrinite reflectance values are higher than 0 5 indicating that the organic matter reached the oil generation window according to the data obtained in this study the abadia montejunto cabacos and brenha formations can be considered potential source rocks of hydrocarbons gas and or oil in this section of the lusitanian basin

rock magnetic properties and relative paleointensity stack between 13 and 24 kyr bp calibrated ages from sediment cores lake moreno patagonia argentina we conducted a detailed study of natural remanence and rock magnetic properties on three sediment cores from lake moreno patagonia argentina based on these measurements we constructed a relative paleointensity stack for the period 13 24 kyr bp calibrated ages rock magnetic properties of the sediment cores showed uniform magnetic mineralogy and grain size suggesting that they were suitable for relative paleointensity studies the remanent magnetisation at 20 mt nrm20 mt was normalised using the anhysteretic remanent magnetisation at 20 mt arm20 mt the saturation of the isothermal remanent magnetisation at 20 mt sirm20 mt and the low field magnetic susceptibility k spectral analysis showed that the normalised records were not affected by local environmental conditions the recorded pseudothellier paleointensity was compared with records obtained from conventional normalising methods comparing the paleointensity curves with others obtained previously in other lakes in the area has allowed us to reach reliable conclusions about centennial scale features 2008 elsevier b v all rights reserved

geochemical characterization of oils and their correlation with jurassic source rocks from the lusitanian basin portugal abstract seeking to identify the oils groups accumulated in the jurassic of the lusitanian basin and the source rock of each group stable carbon isotope and gas chromatography coupled with mass spectrometry analyses were performed in oils and oil shows from the main discoveries and on representative organic extracts from the potential source rocks selected based on previous works and data obtained by total organic carbon and rock eval pyrolysis techniques the geochemical comparison between the oils and between the oils and the organic extracts allowed the identification of three oil groups whose differences depend on their source rocks oils generated at the coimbra formation lower upper sinemurian and accumulated in the same formation and in the agua de madeiros formation upper sinemurian lower pliensbachian in the northern sector of the basin oils originated from the top of the cabacos formation middle oxfordian and accumulated in the montejunto middle upper oxfordian and abadia lower upper kimmeridgian formations in the central and southern sectors of the basin and oil generated and accumulated at the base of the montejunto formation in the central sector of the basin the geochemical correlations between the oils and the organic extracts allowed the identification of the source rocks of the different accumulations of the jurassic succession allowing further guidance to the petroleum exploration in the lusitanian basin

storage of n2 he and ch4 in coal study and application in a practical case in the central asturian coal basin northern spain abstract the behaviour of different gases he n 2 and ch 4 in coal was analyzed using a device for treating raw coal designed for taking samples in the mine this device was subsequently used to transport the samples and inject them with the gases under study experiments were conducted under different pressures and a clear relationship was found between the drop in pressure and the occupation of different storage levels on analysing the pressure evolution it was found that helium rapidly stabilised due to the characteristics of this gas as for the other gases n 2 showed a percentage fall much lower than that of ch 4 in order to compare the storage capacity of different materials with respect to these gases experiments were performed with different materials which form the mine s ceiling and walls it was shown that the fall in pressure is very inferior a fitting equation relating the evolution of pressure with time is proposed which may be used to define the time needed for the gas to stabilize in the coal a normalized equation very similar to that proposed by langmuir is likewise obtained to characterize the adsorption and desorption processes

mineral magnetic study of lacustrine sediments from lake pumoyum co southern tibet over the last 19 ka and paleoenvironmental significance abstract high resolution proxy records from tibetan plateau are essential to understand the past climatic and environmental changes in this work we conducted systematic environmental magnetic studies on lacustrine sediments from lake pumoyum co southern tibet spanning from the last deglaciation 19 ka to present we correlated the magnetic proxies in the lake core with environmental changes the magnetic proxies from the 3 units were studied both unit 3 19 13 2 ka and unit 2 13 2 8 4 ka contain evidences for an anoxic or sub anoxic environment fine grained greigite dominates the bulk magnetic properties of unit 3 while both magnetite and greigite coexist in unit 2 overall this reveals a transition from an anoxic environment to an oxic environment in contrast unit 1 8 4 ka present spans the holocene when the lake environment was oxic there is an increasing trend in the concentration of magnetic minerals which reflects an increasing transport of magnetic minerals from the catchment into the lake due to the increased post glacial melt water flow although different mechanisms affect the magnetic assemblage and associated magnetic properties in the different units our results suggest that the magnetic proxies of the local lake environment on southern tibet are sensitive to environmental changes

characteristics and origins of coal cleat a review abstract cleats are natural opening mode fractures in coal beds they account for most of the permeability and much of the porosity of coalbed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations because permeability and stimulation success are commonly limiting factors in gas well performance knowledge of cleat characteristics and origins is essential for successful exploration and production although the coal cleat literature spans at least 160 years mining issues have been the principal focus and quantitative data are almost exclusively limited to orientation and spacing information few data are available on apertures heights lengths connectivity and the relation of cleat formation to diagenesis characteristics that are critical to permeability moreover recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well studied parameters can yield insight into coal permeability more effective predictions of cleat patterns will come from advances in understanding cleat origins although cleat formation has been speculatively attributed to diagenetic and or tectonic processes a viable mechanical process for creating cleats has yet to be demonstrated progress in this area may come from recent developments in fracture mechanics and in coal geochemistry

lake level fluctuations at ljustjarnen central sweden and their implications for the holocene climate of scandinavia abstract a detailed reconstruction of water level fluctuations in ljustjarnen a small kettle lake in south central sweden provides a preliminary outline of holocene changes in water balance for that region lake levels were generally high from 9200 to 8000 yr b p falling from then until c 6500 6000 yr b p and rising again by 5000 yr b p temporary lowerings were recorded c 4000 yr b p and c 2000 yr b p and water levels have risen dramatically since c 500 yr b p the reconstruction is based on sedimentologic and fossil analyses of multiple cores as well as on geomorphological evidence comparison of lake level fluctuations in south central sweden with those from southern sweden and western finnish lapland and with records of glacier fluctuations in the scandinavian mountains suggest a distinct north south contrast in water balance from 9000 to 5000 yr b p consistent with strongly zonal atmospheric circulation during that period between 7000 and 5000 yr b p the mid holocene dry period appears to have been time transgressive across scandinavia perhaps as a result of a gradual shift in the position of the atlantic polar front and its associated cyclonic stormtrack since 4000 yr b p however most detectable fluctuations are synchronous across scandinavia with the most prominent and widespread change being increased net moisture during the little ice age

historic and paleomagnetic secular variation and the earth s core dynamo process this paper attempts to summarize briefly the recent and ongoing efforts of the geomagnetism and paleomagnetism community to understand both the earth s magnetic field secular variation and its implications for the core dynamo process secular variation is defined in this paper as the general spatio temporal variation of the field secular change will refer to the first time derivative of the spatial field strict geomagnetic definition of secular variation we will emphasize here the long term 10 year or longer behavior of the historic secular variation hsv for this is the variation that is comparable with the paleomagnetic secular variation psv two important related topics the 1969 1970 geomagnetic jerk in secular acceleration and the spatial geomagnetic field components due to crustal or mantle sources are treated more fully in other reviews

early oligocene geomagnetic field behavior from deep sea drilling project site 522 hydraulic piston coring operations at deep sea drilling project site 522 in the south atlantic retrieved an unusually continuous section of late eocene to late oligocene pelagic sediments which we sampled at 3 4 cm intervals 3 5 kyr natural remanent magnetization demagnetization studies indicate a well behaved remanence various rock magnetic procedures strongly suggest the magnetic carrier is dominated by pseudo single domain magnetite appropriate for recording relative intensity variations of the paleomagnetic field nine zones of unusually low relative paleointensity were identified within the 2 my chron c12r interval seven can be typified by a 20 40 kyr interval of low field intensity accompanied by apparently random low amplitude short duration directional fluctuations the other two are of approximately equal duration and intensity but exhibit an orderly progression of directional changes that result in well defined virtual geomagnetic pole vgp paths confined along a preferred meridian of 70 90 w longitude we propose that both styles occur when the main dipole term diminishes significantly but that the former result when undiminished normal secular variation is continuous during the period of low axial dipole moment we propose that the other two lows in relative paleointensity along with one reversal record reflect a field structure of low axial dipole moment dominated by a low degree nonzonal spherical harmonic term alternatively the confined vgp paths could be an artifact of heavy remanence smoothing between nonantipodal semistable transitional geomagnetic pole positions geographical control of vgp paths particularly along 70 90 w longitude has recently been noted for much younger reversals the site 522 record may indicate that the underlying cause of this phenomenon was present at 32 ma we compare our c12r record of paleointensity lows with c12r marine magnetic anomaly tiny wiggles these data appear to indicate that c12r tiny wiggles resulted from periods of low geomagnetic field intensity that were sometimes accompanied by directional excursions

organic facies of the oligocene lacustrine system in the cenozoic taubate basin southern brazil abstract a quantitative study of palynofacies and organic facies was carried out in the cenozoic sedimentary succession of the taubate basin the palaeoenvironmental distributions of particulate organic components were examined in relation to various potential controlling factors lithology depositional environment and stratigraphic sequence about 30 samples were analyzed from a single borehole drilled in sao paulo state this involved rigorous kerogen counts supported by 30 toc and sulphur 20 rock eval pyrolysis and 20 biochemistry analyses in the studied area the oligocene deposits are approximately 600 m thick data was obtained by counting 300 to 500 kerogen particles per sample and then recalculating the percentages of the different constituent groups phytoclast palynomorph and amorphous organic matter aom the kerogen assemblage is palynomorph dominated 70 consisting mainly of freshwater lacustrine algae pediastrum and botryococcus non opaque phytoclasts predominate in most of the kerogen samples however significant variations in the proportion of biostructured and non biostructured brown phytoclasts occur in some intervals the fluorescent aom content occurs in some levels and is composed of two main components an intensively fluorescing structureless organic matter which also has high lipid and protein content indicating a probable bacterial origin for the organic matter microbial mats and terrestrially derived amorphous organic matter which has been reworked to a different extent exhibiting a high content of carbohydrates comparison of the mean kerogen assemblages from different lithologies revealed that the finer grained lithologies generally have higher palynomorph percentages whereas coarser grained lithologies present higher percentages of phytoclasts emphasizing the important role of grain size in organic matter distribution the toc content is generally less than 10 but reaches as high as 44 in some intervals due mainly to the presence of coaly seams the t max spore coloration index and spectral fluorescence measurement values obtained from these samples indicate a low maturity stage the integration of these results together with the organic facies parameters indicate that the analyzed sedimentary section represents a variation from a freshwater lacustrine environment with an oxidant regime to a restricted saline lacustrine environment with a dysoxic anoxic regime there was an excellent correlation between the optical and geochemical parameters

full vector model for magnetization in sediments abstract sediments provide a continuous record of past geomagnetic field variations although it is theoretically possible to get both the direction and intensity of the geomagnetic field from sediment records the mechanism is not fully understood previous workers have postulated that flocculation plays an important role in detrital remanent magnetism drm flocs are porous loose and highly fragile aggregates of microscopic clay particles and their behavior in a viscous medium is likely to be different than single particles of magnetic minerals in order to understand the role of flocculation in sediment magnetization we carried out a set of redeposition experiments at different field intensities and a quasi constant field inclination of 45 we present here a simple numerical model of flocculation incorporating both magnetic and hydrodynamic torques to explain the experimental data at small floc sizes drm acquisition is likely to be non linear in field strengths comparable to the earth s but the sediments may be able to record the directions accurately with increasing floc sizes sediments may retain a record of the intensity that is linearly related to the applied field or a direction parallel to the applied field but are unlikely to do both at the same time also the majority of the magnetic particles in the sediments may not be contributing significantly towards the net drm and any bulk normalizing parameter may be unsuitable if the depositional environment has changed over the depositional period

high resolution paleomagnetic records from laguna potrok aike patagonia argentina for the last 16 000 years 1 holocene and late glacial records documenting variations in direction and intensity of the geomagnetic field during the last 16 000 cal bp are presented for southern patagonia this continuous high resolution terrestrial record from laguna potrok aike 51 58 s 70 23 w was recovered within the salsa south argentinean lake sediment archives and modeling project mineral magnetic measurements indicate that pseudo single domain magnetite is the major carrier of the remanence allowing the reliable determination of stable natural remanent magnetization inclinations and declinations from alternating field demagnetization and principal component analysis paleomagnetic secular variation records reveal most of the familiar features of declination and inclination that have previously been reported in other records from south argentina but conspicuous centennial scale differences are also observed the results illustrate the potential of paleosecular variations records for dating sedimentary sequences in southern south america

a pedogenic model for the magnetic enhancement of late miocene fluvial lacustrine sediments from the xining basin ne tibetan plateau

the magnetic record of particulate pollution in a saltmarsh dee estuary uk in the sediments of a rapidly accreting salt marsh at the head of the dee estuary northwest england magnetic measurements reveal a strong and persistent signal which can be related to the historical effluent discharges of a large iron and steel works the iron oxide content of the pipeline emissions from the works permits their detection by rapid and simple measurements of the weak remanent magnetization of sediments the spatial extent of contamination of the saltings has been determined a clear distance decay effect from the point source has been observed in those parts of the saltings which accumulated during the period of strongest emissions from the plant furthermore down core a marked and spatially consistent spiked magnetic profile has been recorded this distinctive pattern of changes in magnetic concentration and grain size mirrors the past activities and discharges of the works this supposition is corroborated by a supporting chronology based on the record of 137cs emissions from the se

the middle late jurassic forced regression and disconformity in central portugal eustatic tectonic and climatic effects on a carbonate ramp system successions across the middle upper jurassic disconformity in the lusitanian basin west central portugal are highly varied and were probably developed on a large westward inclined hangingwall of a half graben the disconformity is preceded by a complex forced regression showing marked variations down the ramp and provides an example of the effects of rapid relative sea level falls on carbonate ramp systems in the east middle jurassic inner ramp carbonates candeeiros facies are capped by a palaeokarstic surface veneered by ferruginous clays or thick calcretes in the west mid outer ramp marls and limestones brenha facies are terminated by two contrasting successions 1 a sharp based carbonate sandbody capped by a minor erosion surface overlain by interbedded marine lagoonal deltaic deposits with further minor erosion exposure surfaces 2 a brachiopod rich limestone with a minor irregular surface overlain by marls lignitic marls with marine and reworked non marine fossils and charophytic limestones with further minor irregular surfaces and capped by a higher relief ferruginous erosional surface the age ranges from late bathonian in the east to late callovian in the west this disconformity assemblage is succeeded by widespread lacustrine lagoonal limestones with microbial laminites and evaporites cabacos facies attributed to the middle oxfordian over the whole basin increasingly marine facies were deposited afterwards in middle jurassic inner ramp zones in the east the overall regression is marked by a major exposure surface overlain by continental sediments in middle jurassic outer ramp zones to the west the regression is represented initially by open marine successions followed by either a sharp marine erosion surface overlain by a complex sandbody or minor discontinuities and marginal marine deposits in both cases capped by the major lowstand surface reflooding led to a complex pattern of depositional conditions throughout the basin from freshwater and brackish lagoonal to marginal and shallow marine settings additional complications were produced by possible tilting of the hangingwall of the half graben the input of siliciclastics from westerly sources and climate change from humid to more seasonally semi arid conditions the middle late jurassic sea level fall in the lusitanian basin is also recorded elsewhere within the iberian and other peri atlantic regions and matches a transgressive to regressive change in eustatic sea level curves indicating that it is related in part to a global event

carbon sulfur iron relationships and δ13c of organic matter for late albian sedimentary rocks from the north atlantic ocean paleoceanographic implications abstract cores from six deep sea drilling project sites 367 369 137 386 387 and 603 of the late albian north atlantic ocean were investigated for organic carbon content 13c values of the kerogens maceral composition of the organic matter c s ratios fe toc s relationships and framboidal pyrite size distribution in order to evaluate processes that led to the accumulation of organic matter rich black shale deposits the results show a clear separation of the albian north atlantic into an anoxic eastern part and a mostly oxic western part the eastern north atlantic is dominated by organic matter rich deposits sulfate reduction occurred in an oxygen free water column and resulted in characteristic c s ratios fe toc s relationships and framboidal pyrite size distribution patterns elevated productivity anoxia and high sedimentation rates supported the formation of black shale deposits for most of the western and central parts organic matter sedimentation took place through an oxygenated water column the accumulated organic matter is dominantly of terrigenous origin the deposition of marine derived organic matter was most likely controlled by productivity paleobathymetry and low sedimentation rates

paleomagnetic rock magnetic and geochemical study of the 1755 tsunami deposit at boca do rio algarve portugal abstract a multiproxy study combining paleomagnetic rock magnetic magnetic susceptibility anhysteretic remanent magnetization arm isothermal remanent magnetization irm anisotropy of magnetic susceptibility ams and geochemical xrf data was carried out on trench sediments collected in the area of boca do rio algarve south portugal known to have been stricken by a tsunami wave related to the 1755 lisbon earthquake the magnetic mineral assemblage is dominated by multidomain ferrimagnetic grains with a significant contribution 5 9 of ultra fine magnetic particles related to the presence of pedogenetic magnetite the variable amount of this post depositional magnetite plays a role on the characteristic remanent magnetization chrm of the sediment the primary magnetization recorded at t1 located farthest from the coast is representative of the paleosecular variation of the earth s magnetic field and a comparison of the results with the regional model for the geomagnetic field in europe scha dif 3k was used to constrain the erosional signature of the tsunami layer the result indicates that less than eighty years could be missing in the sedimentary column the eroded sediment thickness 27 40 cm was incorporated in the tsunami layer that is characterized by a low magnetic content and a large increase in the ca content representing allochthonous material sedimentological geochemical magnetic and ams data show that the signature of the tsunami layer reflects at least two waves with an erosive capacity that is controlled by the distance from the shore

late paleozoic remagnetization and its carrier in the trenton and black river carbonates from the michigan basin paleomagnetic study of subsurface samples of the upper ordovician trenton and black river limestones collected from six industrial wells in the southern part of the michigan basin yields a well clustered characteristic direction mean dec inc of 170 6 10 9 alpha 95 7 6 circ after rotation of random declinations by aligning a present day field overprint with geographic north the corresponding paleomagnetic pole at 52 4 n 111 0 e is similar to those of the remagnetized carbonates in ontario and new york state suggesting that the michigan formations were also remagnetized in the late paleozoic rock magnetic characterizations suggest that the characteristic magnetization is carried by single and pseudosingle domain magnetite grains very fine rounded single crystal magnetite grains believed to be products of chemical precipitation observed by scanning and scanning transmission electron microscope sem stem are inferred to be the carrier of the remagnetization paired carbon isotope analys

the depositional evolution of diapir and fault bounded rift basins examples from the lusitanian basin of west iberia new data on the evolution of rift basins is presented after analysing the late jurassic stratigraphy of the central lusitanian basin west iberia well outcrop and regional 2d seismic reflection profiles are used to investigate the differences in stratigraphic signature between diapir and fault bounded sub basins during the late jurassic syn rift phase surface rupturing in fault bounded sub basins resulted in the formation of tectonic scarps from which footwall derived gravity flows were sourced in contrast the diapir bounded bombarral alcobaca sub basin evolved as a distal bowl shaped depocentre with an axis located up to 10 km away from its basin margins low gradient marginal slopes developed in the bombarral alcobaca sub basin during the late jurassic rifting while growing salt pillows limited the vertical propagation of basement normal faults differences in tectonic evolution basin physiography and sediment input are the main factors responsible for the distinct sedimentary evolutions recorded in the study area 1 transverse footwall derived sediment fans predominant in fault bounded regions give place to axial southwards prograding fluvial to shallow marine units in the diapir bounded sub basins 2 growing salt pillows absent in the fault bounded sub basins formed barriers to and limited the development of transverse drainage systems

use of magnetic and radiometric measurements to investigate erosion and sedimentation in a british upland catchment in response to the potential shortcomings of single technique strategies in the investigation of erosion and sedimentation a combined magnetic and radiometric 13cs and 210pb approach has been undertaken in the upland watershed lake system of howden reservoir derbyshire by combining these techniques some assessment of sediment sources and the erosion status of the catchment has been achieved alone each approach would have been unable to determine unequivocally sediment provenance furthermore the parallel use of these measurements has highlighted limitations and or uncertainties in both the magnetic and 137cs techniques these problems reflect the particular soil characteristics and drainage conditions of this upland catchment despite the documented severity of peat erosion in the region howden reservoir has a mixture of sediment sources and a relatively moderate rate of sedimentation sediment yields total 127 7 t km 2 yr 1 including organic fraction 31 3 t km 2 yr 1 are however higher than in other british upland areas

the upper and lower thvera sedimentary geomagnetic reversal records from southern sicily detailed paleomagnetic records of the upper and lower thvera polarity transitions have been determined from pliocenc marine marls in southern sicily the dominant magnetic mineral is fine grained magnetite the two transitions have vgp paths following a great circle passing south america and the west coast of north america there are strong indications that the vgp paths result from smoothing of the non antipodal stable directions before and after the transitions the upper thvera transitional record is preceded by two excursions and followed by a third one the first excursion is a sedimentary artefact caused by post depositional migration of magnetic minerals and the third one by is caused by weathering of the sediment the upper thvera transition from sicily is compared with the record from calabria about 250 km away the two records show similarities as well as differences both transitions have identical vgp paths but in calabria the transition is recorded lower in the sediment the first and third excursions have different characters and the second one is not present apparently the registration of transitions of the earth s magnetic field in sediments is strongly influenced by smoothing and diagenetic processes after deposition

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

instantaneous outbursts in underground coal mines an overview and association with coal type instantaneous outbursts in underground coal mines have occurred in at least 16 countries involving both methane ch4 and carbon dioxide co2 the precise mechanisms of an instantaneous outburst are still unresolved but must consider the effects of stress gas content and physico mechanical properties of the coal other factors such as mining methods e g development heading into the coal seam and geological features e g coal seam disruptions from faulting can combine to exacerbate the problem prediction techniques continue to be unreliable and unexpected outburst incidents resulting in fatalities are a major concern for underground coal operations gas content thresholds of 9 m 3 t for ch4 and 6 m 3 t for co2 are used in the sydney basin to indicate outburst prone conditions but are reviewed on an individual mine basis and in mixed as situations data on the sorption behaviour of bowen basin coals from australia have provided an explanation for the conflicting results obtained by coal face desorption indices used for outburst proneness assessment a key factor appears to be different desorption rates displayed by banded coals which is supported by both laboratory and mine site investigations dull coal bands with high fusinite and semifusinite contents tend to display rapid desorption from solid coal for a given pressure drop the opposite is true for bright coal bands with high vitrinite contents and dull coal bands with high inertodetrinite contents consequently when face samples of dull fusinite or semifusinite rich coal of small particle size are taken for desorption testing much gas has already escaped and low readings result the converse applies for samples taken from coal bands with high vitrinite and or inertodetrinite contents in terms of outburst potential it is the bright vitrinite rich and the dull inertodetrinite rich sections of a coal seam that appear to be more outburst prone this is due to the ability of the solid coal to retain gas even after pressure reduction creating a gas content gradient across the coal face sufficient to initiate an outburst once the particle size of the coal is reduced rapid gas desorption can then take place c 1998 elsevier science

deciphering the impact of diagenesis overprint on negative δ13c excursions using rock magnetism case study of ediacaran carbonates yangjiaping section south china rock magnetism is used here to investigate the genesis of one of the puzzling negative carbon isotopic excursions of the neoproterozoic in the yangtze platform south china a detailed characterization of the magnetic mineralogy which includes low temperature and high field magnetometry and classical magnetic measurement arm irm susceptibility was therefore performed along upper doushantuo and lower dengying formations outcropping in the yangjiaping section the derived magnetic parameters show variations that can be interpreted as variations in magnetic grains size and in oxide contents they show that the magnetic content is significantly reduced in samples presenting negative 13ccalcite values we interpret this as a result of magnetite dissolution and secondary carbonate precipitation during early diagenesis bacterial sulfate reduction combined with c and o isotopic data paleomagnetic techniques thus show that the upper doushantuo lower dengying negative excursion of the yangjiaping section is largely due to diagenesis although the preservation of a genuine 13c excursion of lower magnitude from 7 down to 0 instead of down to 9 as usually considered cannot be ruled out a corrected 13ccarbonate chemostratigraphic curve is therefore proposed the unambiguous identification of a strong diagenetic component for this excursion casts doubts on the primary nature of other potentially time equivalent negative excursions of the yangtze platform and thus to its correlation to negative excursions in other cratons i e shuram excursion more generally this study illustrates the potential of magnetic mineralogy characterization a low cost time efficient and non destructive technique as screening tool for diagenetic overprints of 13c and 18o

solid bitumen occurrences in the arruda sub basin lusitanian basin portugal petrographic features abstract the middle jurassic to cretaceous sedimentary record in the lusitanian basin portugal reveals the presence of disseminated solid bitumen the present work is focused on the petrographic characteristics of solid bitumen identified in the freixial 1 and benfeito 1 boreholes arruda sub basin lusitanian basin that display different thermal maturities microscopy techniques reflected and transmitted white light incident blue light and sem and organic geochemistry analyses total organic carbon total sulfur and insoluble residue were used to study these samples from the results obtained by optical microscopy fluorescence and reflectance it was possible to distinguish three types of solid bitumen they were labeled as solid bitumen a present in all the samples solid bitumen b and solid bitumen c these ones observed in some of them they correspond to allochthonous migrated bitumens in blue incident light some bitumen do not show fluorescence while others reveal fluorescence that range from yellow solid bitumen b to dark brown solid bitumen a all bitumens are optically isotropic bitumen reflectance varies between 0 70 and 2 60 r r and the vitrinite reflectance ranges from 1 11 to 1 48 r r based on the r r values the solid bitumen identified in these samples are classified as impsonite epi and cata or pyrobitumen no relation can be established with confidence for the reflectance of bitumens with the reflectance of vitrinite

the different climatic response of pedogenic hematite and ferrimagnetic minerals evidence from particle sized modern soils over the chinese loess plateau abstract in recent years increasing interest in loess studies has focused on qualitative and quantitative paleoclimatic reconstruction using the imperfect antiferromagnetic mineral hematite however the linkage between the hematite formation and climatic variables remains controversial here we present the results of a comprehensive investigation of the magnetic properties and statistical analysis of a suite of clay and silt fractions of modern soil samples from 179 sites across the chinese loess plateau clp and adjacent regions our objective was to clarify the relationships between modern climatic variables and pedogenic hematite as well as pedogenic ferrimagnetic minerals first order reversal curve measurements were also conducted on representative particle sized subsamples from a n s transect to understand the differences in magnetic mineralogy between the two fractions our results show that pipette extraction separates the fine grained superparamagnetic sp and most of the single domain sd magnetic grains into the clay fraction and that the remaining silt fraction displays the magnetic properties of coarse pseudo single domain psd or a mixture of multidomain md psd and a few sd particles only the pedogenic clay fraction shows a strong correlation with climatic variables the application of redundancy analysis helps to distinguish the climate variables controlling the formation of ferrimagnetic minerals and hematite during pedogenesis on the clp pedogenic ferrimagnetic minerals are sensitive to mean annual precipitation while pedogenic hematite formation is preferentially dependent on mean annual temperature the confirmation of the temperature dependent nature of hematite on the clp provides a new possibility for quantitatively reconstructing the paleotemperature history of chinese loess paleosol sequences

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

seismic and sedimentologic features of oxfordian kimmeridgian syn rift sediments on the eastern margin of the lusitanian basin following deposition of widespread middle oxfordian lacustrine carbonates and evaporites the lusitanian basin was differentiated into a number of sub basins the arruda sub basin is a half graben basin situated some 30 km north of lisbon it accumulated over 2 5 km of kimmeridgian siliciclastic sediments and is bounded to the east by the vila franca de xira fault zone carbonate deposition persisted over horsts along the fault zone from the oxfordian to the early kimmeridgian and in places to the late kimmeridgian and shows a pronounced west east facies zonation with higher energy framestones and grainstones accumulating along the exposed western margins seismic data indicate a major gap between the horst blocks that acted as a conduit through which basement derived siliciclastics were fed westwards into the sub basin to form a submarine fan system the presence of large blocks of framestone carbonates encased in siliciclastics indicates that carbonate sedimentation occurred in abandoned parts of the fan system the rapid changes of sediment thicknesses and facies types along the eastern margin of the arruda sub basin are indicative of contemporaneous strike slip movements

analysis of a 150 m sediment core from the co seismic subsidence depocenter of the 2009 mw 6 1 l aquila earthquake italy implications for holocene pleistocene tectonic subsidence rates and for the age of the seismogenic paganica fault system abstract laqui core was drilled in the co seismic subsidence depocenter shown by dinsar images in the bazzano sub basin after the 2009 mw 6 1 l aquila earthquake laqui core aimed at gathering high resolution integrated stratigraphy and defining its relationships with the paganica and other active faults that yielded co seismic subsidence lithostratigraphy and micropaleontological analyses indicate a late pleistocene holocene fluvial alluvial sequence and below 41 m palustrine sediments sandwiching at 84 115 m a thick gravel package four 14c ages gathered from 5 to 15 m yield calibrated ages between 6 and 41 ka bp paleomagnetism reveals a normal polarity above 84 m while below the gravel package 115 m it shows frequent polarity changes the occurrence of intervals of clear reverse polarity testifies below 115 m the deposition during the matuyama chron we conclude that the normal polarity package down to 84 m along with the underlying gravels were deposited at high sedimentation rate 0 46 mm yr for the upper 15 m during the brunhes chron

absolute paleointensities between 60 and 160 kyear bp from mount etna sicily abstract paleointensity measurements were conducted on 17 distinct lava flows from mount etna sicily in order to obtain records of absolute paleointensities for the period covering the last 60 160 kyear a complementary aspect of this study was to improve and extend the calibration of relative paleointensities obtained for the same interval from sedimentary sequences based on absolute values of virtual axial dipole moments seventy three samples have been subjected to double heating thellier coe experiments under vacuum and care was taken to perform additional studies dealing with the magnetic mineralogy and to scrutinize the effects of heating upon magnetic minerals potassium argon k ar datings provided precise ages in most cases absolute paleointensities were obtained with success for ten lavas flows the succession of the virtual axial geomagnetic dipoles vadm oscillate between extrema centered around a mean value of 6 3 2 6 10 22 a m 2 this result is in good agreement with the sedimentary record published for the same period and confirms that there has been an appreciable decrease in geomagnetic field intensity between 80 and 150 kyear

palaeointensities from sediments normalization by laboratory redepositions abstract deep sea sediments comprising small magnetic grains in coarse and fine fabrics were reconstituted and deposited in laboratory fields both the magnitude and the direction of the natural remanent magnetization nrm were accurately reproduced only the middle coercivity fraction however gave a faithful representation of the laboratory field this same fraction originally held the stable nrm component the results were interpreted on a model of post depositional realignment based on the physical characteristics of the sediment laboratory redeposition was found to be a closer analogue to the nrm than were anhysteretic or other laboratory induced magnetizations guidelines are given by which the techniques could be utilised to estimate the intensity of the ancient geomagnetic field

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

aspects of the structural evolution of the lusitanian basin in portugal and the shelf and slope area offshore portugal abstract the study provides a regional seismic interpretation and mapping of the mesozoic and cenozoic succession of the lusitanian basin and the shelf and slope area off portugal the seismic study is compared with previous studies of the lusitanian basin from the late triassic to the cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence the triassic rifting was concentrated in the central part of the lusitanian basin and in the southernmost part of the study area both as symmetrical grabens and half grabens the evolution of half grabens was particularly prominent in the south the triassic fault controlled subsidence ceased during the latest late triassic and was succeeded by regional subsidence during the early early jurassic hettangian when deposition of evaporites took place a second rift phase was initiated in the early jurassic most likely during the sinemurian pliensbachian this resulted in minor salt movements along the most prominent faults the second phase was concentrated to the area south of the nazare fault zone and resulted here in the accumulation of a thick sinemurian callovian succession following a major hiatus probably as a result of the opening of the central atlantic resumed deposition occurred during the late jurassic evidence for late jurassic fault controlled subsidence is widespread over the whole basin the pattern of late jurassic subsidence appears to change across the nazare fault zone north of the nazare fault fault controlled subsidence occurred mainly along nnw sse trending faults and to the south of this fault zone a nne ssw fault pattern seems to dominate the oxfordian rift phase is testified in onlapping of the oxfordian succession on salt pillows which formed in association with fault activity the fourth and final rift phase was in the latest late jurassic or earliest early cretaceous the jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones however only salt pillow development can be demonstrated the extensional tectonics ceased during the early cretaceous during most of the cretaceous regional subsidence occurred resulting in the deposition of a uniform lower and upper cretaceous succession marked inversion of former normal faults particularly along ne sw trending faults and development of salt diapirs occurred during the middle miocene probably followed by tectonic pulses during the late miocene to present the inversion was most prominent in the central and southern parts of the study area in between these two areas affected by structural inversion fault controlled subsidence resulted in the formation of the cenozoic lower tagus basin northwest of the nazare fault zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed the miocene compressional stress was mainly oriented nw se shifting to more n s in the southern part

palynofacies and organic geochemistry of the sinemurian carbonate deposits in the western lusitanian basin portugal coimbra and agua de madeiros formations abstract the lower jurassic in the lusitanian basin portugal is mainly represented by hemipelagic carbonated deposits rich in organic matter om in this study supported by a high resolution stratigraphic and sedimentological framework the analysis of the om content of the coimbra and agua de madeiros formations in the reference outcrop sections of s pedro de moel and peniche is presented this is a multidisciplinary approach to the study of 31 samples in these series supported by organic petrography palynofacies spore coloration index sci and random vitrinite reflectance rr and organic geochemistry total organic carbon toc and biomarkers the palynofacies analysis provides evidence that the om is mainly composed of particles belonging to the amorphous organic matter aom group the phytoclasts correspond mostly to the non opaque translucent subgroup generally degraded and oxidized with significant representation in some stratigraphic levels of the coimbra formation and the polvoeira member at peniche the palynomorphs are mainly composed of classopollis pollen grains zygospores acritarchs and prasinophyte phycomata the toc data confirm that most samples are om rich with some stratigraphic horizons of the coimbra formation reaching 8 8 wt the predominance of marine om was confirmed by the pr nc17 and ph nc18 ratios the pr fi and homohopane ratios c35 c34 indicate that some stratigraphic horizons were deposited under dysoxic anoxic conditions despite the organic rich nature of these two units the random vitrinite reflectance rr 0 45 the spore coloration index 3 0 4 0 and the presence of hopanes suggest that these rocks in terms of om maturity are thermally immature

paleomagnetic secular variation and relative paleointensity during the holocene in south china huguangyan maar lake revisited the scarcity of reliable paleomagnetic secular variation psv records from east asia especially from low latitude regions impedes better understanding of global psv mechanisms here we report on a radiocarbon dated holocene psv record from a composite 6 7 m long core collected from the high sedimentation rate huguangyan maar lake hml in subtropical tropical south china rock magnetic results demonstrate that the natural remanent magnetization resides in single domain magnetite alternating field demagnetization experiments at 1 cm spacing on u channel samples reveal six distinct inclination highs at 7 500 bce 5 100 bce 4 600 bce 3 600 3 400 bce 1 600 1 200 bce and 600 800 ce three inclination lows at 4 800 bce 600 300 bce and 1 000 1 300 ce and three eastward declination trends at 3 600 3 200 bce 2 600 2 400 bce and 400 bce to 200 ce the similarity between the hml psv record and other independently dated records from east asia and geomagnetic field models corroborates the robustness of our age model and holocene psv record strikingly centennial to millennial scale psv features of the hml are comparable within age uncertainties with other holocene records from europe north america and canada suggesting that such directional patterns are likely to be hemispheric in scale although relative paleointensity data of hml are affected by environmental factors e g organic matter diagenesis the record still provides a regionally important new psv reference curve whose conspicuous features may serve as stratigraphic markers for east asian paleorecords

comparison of hysteresis thermomagnetic and low temperature magnetic properties of particle size fractions from loess and palaeosol samples in central asia and the chinese loess plateau

equatorial and mid latitude records of the last geomagnetic reversal from the atlantic ocean abstract three records of the matuyama brunhes reversal have been obtained from odp deep sea cores distributed along the west african margin in the atlantic ocean these studies in addition to the record from dsdp site 609b provide a latitudinal transect extending from the equator to 50 n simulations of natural smoothing by post depositional processes show that characteristic features of a transitional field geometry dominated by axisymmetry should be preserved in the records especially at the equator the results do not seem to favour the hypothesis that axisymmetrical terms would dominate during this transition