extinct mountain goat oreamnos harringtoni in southeastern utah the extinct harrington s mountain goat oreamnos harringtoni stock is predominantly known from dry cave localities in the grand canyon arizona in addition to two sites in the great basin nevada and from san josecito cave nuevo leon mexico a dry shelter in natural bridges national monument on the central colorado plateau southeastern utah preserves numerous remains of the extinct mountain goat in addition to pack rat middens remains from a 100 cm stratigraphic profile indicate that o harringtoni lived on the plateau 39 800 yr b p the oldest directly dated find of extinct mountain goat plant macrofossils indicate that engelmann s spruce picea engelmannii limber pine pinus flexilis rose rosa cf woodsii and douglas fir pseudotsuga menziesii grew during the late pleistocene where a riparian and a pinyon juniper pinus edulis juniperus osteosperma community now predominates douglas fir are found only in mesic protected north facing areas limber pine douglas fir bark and grasses were the major dietary components in the dung a springtime diet of birch betula is determined from pollen clumps in dung pellets

late quaternary vertebrates from the upper gunnison basin colorado and small mammal community resilience to climate change since the last glacial maximum the upper gunnison basin ugb colorado is a montane region characterized by unusual physiography and topographic isolation excavations of three caves in the ugb provide one of the most diverse records of high elevation late quaternary vertebrates in north america the localities haystack cave 2450 m above sea level m asl cement creek cave 2860 m asl and signature cave 3055 m asl together provide a near continuous record of vertebrate communities that extends from before the last glacial maximum to the present these communities largely represent a sagebrush artemisia spp steppe tundra environment that prevailed throughout the ugb in the late pleistocene at least five taxa of extinct large mammals disappear from the ugb by the early holocene one small mammal the short faced skunk brachyprotoma cf b brevimala also became extinct the fossil record further indicates that only four small extant mammals sorex preblei dicrostonyx sp lemmiscus curtatus and urocitellus elegans were extirpated from the ugb by the early holocene in part because of community restructuring and loss of open habitats with expansion of forests to higher elevations an analysis of taxonomic richness and evenness at cement creek cave indicates high resilience in the small mammal community despite major climate shifts over the past 40 000 yr

sedimentation rate control on diagenesis east china sea sediments abstract diagenesis of ferrimagnetic minerals can alter the magnetic properties erasing partially or entirely the original paleomagnetic and paleoclimatic signals especially on continental margins where sedimentation rates are usually high understanding the mechanisms by which magnetic particles are affected by diagenesis is therefore critical for retrieving paleomagnetic and paleoclimatic information from sediments high resolution magnetic analysis was carried out on rapidly deposited 0 4 20 mm year holocene sediments from the east china sea ecs inner continental shelf the primary magnetic mineral assemblage in the sediment core contains ferrimagnetic minerals such as magnetite with minor contributions from hematite the magnetic properties vary down core in two steps due to post depositional reductive diagenesis the first occurs at depths of 0 15 1 1 m and is characterized by reduction of both magnetite and hematite in suboxic sediments the suboxic sulfate boundary ssb is therefore located at 1 1 m we demonstrate that the depth of the ssb has negative relation to the average sedimentation rate in chinese marginal seas the second step change in magnetic properties occurs at 3 2 5 8 m and contains two intervals with extremely low magnetic mineral content each corresponding to dissolution fronts associated with the former and present position of the sulfate methanic transition smt these two intervals correlate well with abrupt changes in sedimentation rate and separate the anoxic zone into two parts the sulfidic zone and the methanic zone our study suggests that sedimentation rate provides a dominant control on magnetic mineral diagenesis at least in the chinese marginal seas which controls not only the type of redox zonation but also the thicknesses of diagenetic zones

low concentration of heavy metals in the yangtze estuarine sediments china a diluting setting abstract an examination of the spatial and temporal distribution of 17 major heavy metals i e fe zn ni mg co mn etc was made in the yangtze estuarine sediments revealed by a number of vibrocores taken from the different sediment zones including delta front prodelta and delta shelf transition the results obtained from the numerous core samples which were also measured for pb 210 and cs 137 show that 1 the silty clay comprising the prodelta facies serves as a depositional sink attracting high concentrations of heavy metals delivered from the river mouth 2 after being normalized to aluminum as a proxy for grain size most heavy metals presented in the prodelta facies have lower concentrations than in the other adjacent sediment zones 3 also after normalization concentrations of most heavy metals in the vibrocore sediments tend to increase up core and 4 sedimentation rates in the study area range from 2 0 to 6 0 cm a hence the vibrocores contain a sedimentary record of metal deposition covering more than 50 years it has previously been assumed that sediments off the river mouth were heavily polluted due to industrialization of the shanghai metropolitan area which peaked about 50 years ago however the low concentrations of heavy metals in the study area before and after normalization do not support this assumption the yangtze estuary is characterized largely by the tremendous runoff and unpolluted sediments derived from the upper drainage basin to constitute a unique diluted setting in which the dispersal behavior of heavy metals from the adjacent industrialized coast is influenced substantially as a result the heavy metals in the study area are obviously lower than those previously determined along the coast

diagenetic modulation of the magnetic properties in sediments from the northern indian ocean 1 large changes in magnetic mineral concentration dependent parameters by more than 1 order of magnitude occur over 50 150 cm intervals in two marine sediment cores from the oxygen minimum zone in the gulf of aden high resolution sedimentological and chemical analyses indicate that these intervals are not associated with turbiditic events or sediment reworking they do not result from changes in carbonate dilution or differences in sediment properties and they do not correspond to volcanic layers magnetic mineralogical analyses reveal a change in magnetic mineral concentration from a magnetite goethite assemblage to pure magnetite within the peak the peaks almost disappear when the abundance of magnetic minerals is calculated after correcting for the magnetic moments of each magnetic mineral therefore under the assumption that the variability of the magnetic parameters results from postdepositional mineralogical transformations a relatively constant amount of magnetite was present at the surface of the sediment changes in redox conditions and nonsteady state diagenesis transformations have effectively been observed along both cores large values of total organic carbon coincide with poor preservation of biogenic and detrital magnetite which reflects reductive dissolution of the finer magnetite grains at the same levels fe 2 release from reductively dissolved magnetite favored precipitation of goethite the susceptibility peaks coincide with episodes of magnetite preservation caused by reduced surface

reductive diagenesis magnetite dissolution greigite growth and paleomagnetic smoothing in marine sediments a new view abstract in many anoxic sedimentary environments the onset of sulfate reduction and pyritization of detrital iron bearing minerals leads to a precipitous decline in magnetic mineral concentration during early diagenesis the usefulness of the surviving paleomagnetic record in such environments is usually argued to depend on how much of the primary detrital magnetic assemblage survives diagenetic dissolution detailed rock magnetic and electron microscope analyses of rapidly deposited 7 cm kyr latest pleistocene holocene sediments from the continental margins of oman 22 22 4 n 60 08 0 e and northern california 38 24 8 n 123 58 2 w demonstrate that pyritization during early diagenesis also leads to the progressive down core growth of the ferrimagnetic iron sulfide greigite greigite growth begins with nucleation of large concentrations of superparamagnetic sp nanoparticles at the inferred position of the sulfate methane transition which can explain the apparently paradoxical suggestion that diagenetically reduced sediments contain enhanced concentrations of sp particles looping of hysteresis parameters on a day plot records the dissolution of single domain sd titano magnetite and the formation of sp greigite which then slowly and progressively grows through its sd blocking volume and acquires a stable paleomagnetic signal this looping trend is also evident in data from several published records oregon margin korea strait japan sea niger fan argentine margin and the ontong java plateau indicating that these processes may be widespread in reducing environments our observations have profound implications for paleomagnetic records from sulfate reducing environments the paleomagnetic signal recorded by greigite is offset from the age of the surrounding sediments by 10 s of kyr and ongoing growth of greigite at depth results in smoothing of the recorded signal over intervals of 10 s to 100 s of kyr we therefore expect the presence of greigite to compromise paleomagnetic records in a wide range of settings that have undergone reductive diagenesis

particle size related mineral magnetic source sediment linkages in the rhode river catchment maryland usa characterization of both the source materials and the bottom sediments of an estuary by magnetic characters on a particle size basis allows the source of the bottom sediments to be determined and indicates a shift in sediment sources corresponding to changing land use patterns the major source of the sediments in the lower part of cores from the middle of the estuary is eroding shorelines soil derived particulates from the uplands dominate the upper part of the cores this change in source occurred in the early part of the 19th century the magnetic character of the most recent sediments suggests a progressive depletion through time of the upland soils in the finest fractions

rock magnetism and geochemistry of two plio pleistocene chinese loess palaeosol sequences implications for quantitative palaeoprecipitation reconstruction abstract stratigraphic and spatial variations in the magnetic properties of chinese loess are widely accepted as reflecting changes in the intensity of soil forming processes over time and space recently several workers have used statistical correlations between the magnetic susceptibility and related parameters of modern loess plateau soils and modern climate to generate transfer functions to reconstruct past temporal and spatial trends in precipitation here we try to assess the viability of this approach by conducting magnetic and geochemical measurements of two long 2 5 my loess palaeosol sequences from different locations on the modern precipitation gradient across the loess plateau one site duanjiapo is located on the southern humid margin of the plateau and the other site luochuan is located in a drier modern environment some 160 km further north our results indicate discrepancies between magnetic and geochemical indicators of weathering and soil forming intensity and that any attempt to predict palaeoprecipitation at duanjiapo using published approaches would be significantly in error overall our results indicate a complex response of magnetic mineral transformations to climate including the production of both ferrimagnetic and antiferromagnetic minerals within the same climatic interval together with the destruction of magnetic material within some of the palaeosols therefore we suggest considerable caution should be exercised in generating quantitative climatic reconstructions from a single magnetic parameter

links between bulk sediment particle size and magnetic grain size general observations and implications for chinese loess studies using a combination of particle size analysis magnetic measurements scanning electron microscopy and transmission electron microscopy imaging this study shows that in a wide range of depositional environments there is a strong link between particle size classes and magnetic response especially below the upper limit of stable single domain magnetic behaviour ferrimagnetic grain assemblages dominated by stable single domain magnetosomes regularly have peak susceptibility and remanence values in coarser grades than do those containing finer grained viscous and superparamagnetic secondary magnetic minerals formed during pedogenesis this effect is despite the fact that there is a one to two orders of magnitude size difference between the particle size boundaries at 1 or 2 m and key domain state transitions mostly below 0 05 m the implications of these results are explored using samples spanning 22 myr of loess accumulation on the chinese loess plateau the results from the loess sections complemented by data from low temperature magnetic experiments show that there are subtle distinctions in mean ferrimagnetic grain size between the pleistocene and miocene parts of the record thus allowing more refined rock magnetic interpretations of the fine grained ferrimagnetic mineral assemblages arising from the effects of weathering pedogenesis and possibly diagenesis in the sections studied

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

magnetic mineral diagenesis in the river dominated inner shelf of the east china sea china the inner shelf of the east china sea is a river dominated margin characterized by fine grained mud deposits and a rapid sedimentation rate three short sediment cores 2 7 m in length were examined to characterize spatial variations in magnetic mineral diagenesis the sediment cores were analyzed for sedimentation rates magnetic properties particle size distribution organic carbon and total sulfur content the two more proximal cores with higher sedimentation rates 2 2 cm yr and 0 96 cm yr do not exhibit obvious effects of reductive dissolution of magnetite with increasing depth which is consistent with their lower total sulfur content the offshore core a12 4 which has a lower sedimentation rate contains clear evidence of magnetite dissolution and increasing total sulfur content with depth the three cores have a similar sediment source and organic matter input therefore we suggest that a higher sedimentation rate will lead to less reductive diagenesis of magnetite assuming that other factors are constant the iron to sulfate reduction boundary i e revealed by the onset of a rapid decline of magnetic susceptibility is located 1 0 m below seafloor in core a12 4 this is much deeper than is reported in many other coastal marine environments and can be explained by the higher sedimentation rate the presence of refractory terrestrial organic matter and an abundant input of detrital iron oxides this study demonstrates that analyses of the magnetic mineral zonation provide a straightforward approach to assess diagenetic organic carbon decomposition pathways in marine environments

flux and fate of yangtze river sediment delivered to the east china sea numerous cores and dating show the yangtze river has accumulated about 1 16 x 10 12 t sediment in its delta plain and proximal subaqueous delta during holocene high resolution seismic profiling and coring in the southern east china sea during 2003 and 2004 cruises has revealed an elongated similar to 800 km distal subaqueous mud wedge extending from the yangtze river mouth southward off the zhejiang and fujian coasts into the taiwan strait overlying what appears to be a transgressive sand layer this distal clinoform thins offshore from similar to 40 in thickness between the 20 and 30 m water depth to 1 2 in between 60 and 90 m water depth corresponding to an across shelf distance of less than 100 km total volume of this distal mud wedge is about 4 5 x 10 11 m 3 equivalent to similar to 5 4 x 10 11 t of sediment most of the sediment in this mud wedge comes from the yangtze river with some input presumably coming from local smaller rivers thus the total yangtze derived sediments accumulated in its deltaic system and east china sea inner shelf have amounted to about 1 7 x 10 12 t preliminary analyses suggest this longshore and across shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid holocene highstand and after re intensification of the chinese longshore current system sedimentation accumulation apparently increased around 2000 yrs bp reflecting the evolution of the yangtze estuary and increased land erosion due to human activities such as fanning and deforestation the southward flowing china coastal current the northward flowing taiwan warm current and the kuroshio current appear to have played critical roles in transporting and trapping most of yangtze derived materials in the inner shelf and hence preventing the sediment escape into the deep ocean c 2006 elsevier b v all rights reserved

high resolution analysis of early diagenetic effects on magnetic minerals in post middle holocene continental shelf sediments from the korea strait 1 two studied sediment cores from the korea strait contain mud sequences 14 m and 32 62 m in thickness that were deposited during the last 6 000 years the sediments have uniform lithology and geochemical properties however marked down core changes in magnetic properties suggest that diagenesis has significantly impacted the magnetic properties an expanded view of early diagenetic reactions that affect magnetic mineral assemblages is evident in these rapidly deposited continental shelf sediments compared to deep sea sediments the studied sediments are divided into four descending intervals based on magnetic property variations interval 1 is least affected by diagenesis and has the highest concentrations of detrital magnetite and hematite and the lowest solid phase sulfur contents interval 2 is characterized by the presence of paramagnetic pyrite and sharply decreasing magnetite and hematite concentrations which suggest active reductive dissolution of detrital magnetic minerals interval 3 is marked by a progressive loss of hematite with depth and coincides with the minimum magnetite concentration interval 4 has an increasing down core enhancement of authigenic greigite which apparently formed at depths of 3 30 m below the sediment water interface due to arrested pyritization reactions these results indicate delays of thousands of years for acquisition of magnetizations carried by greigite which suggests that studies of geomagnetic field behavior from greigite bearing continental shelf sediments should be conducted with care also virtually complete destruction of detrital magnetic minerals at depth suggests that magnetic studies of rapidly deposited shelf sediments are unlikely to provide a meaningful signature associated with syn depositional environmental processes

high resolution record of the upper olduvai transition from po valley italy sediments support for dipolar transition geometry abstract a detailed record of the upper olduvai polarity transition composed of 100 transitional directions has been obtained from the crostolo section in northern italy a careful examination of the rock magnetic properties of the sediments using standard paleomagnetic techniques thermomagnetic scanning electron microscopy microprobe x ray diffraction and mossbauer analysis shows that greigite is the main magnetic carrier of the remanence the correlation of a shift in the magnetic record to a small scale sedimentary feature observed in the section indicates that the magnetization was acquired at deposition or very shortly after the virtual geomagnetic pole vgp path is largely confined along a great circle over north and south america 90 west of the site and consists of three stages first the vgp moves to southern mid latitudes then after a period of standstill it comes back to almost true north and finally the south pole is reached in a third step although different from a record from the southern indian ocean this path is virtually identical to those obtained for the same transition from north pacific deep sea cores and partly coincides with a north atlantic record which suggests that a dipolar component may be present in the transitional field during the upper olduvai reversal a review of the recently obtained records of various transitions shows that in more than two thirds of the cases the vgp paths are similarly confined along a meridian over the americas or antipodal to them irrespective of the sampling site and of the sense of the transition although not deterministic this tendency suggests that a similar dipolar component might be present in the transitional fields of other reversals of different ages

burial of terrestrial organic matter in marine sediments a re assessment 1 calculations based on recent observations indicate that approximately one third of the organic matter presently being buried in marine sediments may be of terrestrial origin with the majority of this terrestrial organic matter tom burial occurring in muddy deltaic sediments these calculations further suggest that the remineralization of terrestrial organic matter in the oceans is also much less efficient than that of marine organic matter these two underappreciated observations have important implications in terms of our understanding of the controls on the global carbon cycle from a paleoceanographic perspective the results presented here also suggest that changes in tom burial on glacial interglacial timescales have the potential to impact the global carbon cycle i e atmospheric co2 levels

early diagenesis of magnetic minerals in marine transitional environments geochemical signatures of hydrodynamic forcing abstract the low field magnetic susceptibility of surficial sediments from the ria de pontevedra nw spain shows a characteristic hydrodynamically driven textural control where diamagnetic sandy bioclastic carbonates occur toward the coastline leaving the finer muddy sediments to be deposited in the central and deeper areas of the ria three gravity cores were collected from the inner core 1 middle core 2 and outer core 3 zones of the clayey rich central axis of the ria from which the magnetic properties geochemical characteristics and hydrodynamic regime of the uppermost 90 cm of the sediment record were reconstructed profiles have a distinctive pattern that is controlled by depth isothermal remanent magnetization irm acquisition curves facilitated the identification of three well defined zones with depth depending on their degree of magnetic saturation and thus of their dominant magnetic behaviour magnetite like goethite like and greigite like this zonation is interpreted as the result of mineralogical changes during early diagenesis the relative depths of each zone are mostly dependent on distance to the open sea with the magnetite like zones being thicker in the outermost part of the ria toward the inner part of the ria the three zones become shallower and thinner in the innermost areas only greigite like coercivities are observed good correlation between magnetic and geochemical parameters such as vs 2fe s or h cr vs c s demonstrates that magnetic property variations with depth are diagenetically controlled and that these parameters can be used as magnetic proxies for early diagenesis similar significant positive correlations were found between of the clay fraction and modelled wave heights and between other magnetic and hydrodynamic parameters providing magnetic evidence of cryptic wave climate forcing of the diagenetic pathway the combined analysis of the magnetic geochemical and hydrodynamic data ultimately indicates that the sediment distribution and subsequent diagenetic pathway in this type of transitional environment mostly depend on the local distribution of wave energy and water depth rather than on estuarine like circulation processes

dung of mammuthus in the arid southwest north america abstract the discovery of a unique organic deposit in a dry cave on the colorado plateau southern utah permits the first comparison of the physical characteristics and the diet of the dung of the extinct mammoths from the arid southwest north america with that of mammoths from siberia and northern china the only other known locations of such remains the deposit buried beneath sand and rockfall is composed primarily of mammoth dung estimated at over 300 m3 radiocarbon dates on dung boluses indicate that the mammoths frequented the cave between approximately 14 700 and 11 000 yr b p the range of ages at 2 the desiccated boluses measuring approximately 230 170 85 mm are nearly identical in size to dung from extant elephants the largest contents in the dung are stalks measuring 60 4 5 mm grasses and sedges dominated the diet although woody species were commonly eaten

environmental magnetism of pleistocene sediments in the north pacific and ontong java plateau temporal variations of detrital and biogenic components 1 an environmental magnetic study was conducted to investigate temporal variations of the sources of magnetic minerals in the pacific ocean using sediment cores of pleistocene age the proportion of interacting i to noninteracting n i single domain components was estimated from first order reversal curve diagrams and the proportion of middle m to low l coercivity components was determined from decomposition of isothermal remanent magnetization irm acquisition curves the i and m components are interpreted to be carried by terrigenous maghemite while the n i and l components represent biogenic magnetite an inverse correlation between the ratio of anhysteretic remanent magnetization susceptibility arm to saturation irm sirm and the i n i ratio was confirmed for sediments across wide expanses in the pacific ocean this implies that arm sirm can be used to estimate the relative abundances of biogenic and terrigenous components in sediments in the north pacific the relative abundance of the i and m components increases in glacial periods variations of arm sirm and s ratio s 0 1t resemble each other and decrease in the same time intervals these variations reflect increases of terrigenous input in glacial periods as eolian dust on the ontong java plateau in the western equatorial pacific on the other hand minima in arm sirm and s 0 1t occur at glacial to interglacial transitions and the relative abundance of the i and m components increases in these periods terrigenous material in this region is considered to be transported mainly from the new guinea and solomon islands by the equatorial undercurrent the higher proportion of the terrigenous component at glacial to interglacial transitions is coeval with carbonate preservation maxima reported from the ontong java plateau suggesting a linkage between the two

magnetite dissolution diachronous greigite formation and secondary magnetizations from pyrite oxidation unravelling complex magnetizations in neogene marine sediments from new zealand detailed rock magnetic and electron microscope analyses indicate that the magnetic signature of neogene marine sediments from the east coast of new zealand is dominated by the authigenic iron sulphide greigite the greigite is present as a mixed population of stable single domain and superparamagnetic grains which is consistent with authigenic growth from solution this growth can result from pyritization reactions soon after deposition which also leads to dissolution of most detrital magnetite however where constrained by field tests our data suggest that remanence acquisition can occur 1 myr after deposition and can vary in timing at the outcrop scale strong viscous overprints result from oxidation of the iron sulphides probably during percolation of oxic ground water this process can sometimes destroy any ancient remanent magnetization this complex magnetic behaviour particularly the presence of late forming magnetizations carried by greigite means that the remanence in new zealand cenozoic sediments and in similar sediments elsewhere cannot be assumed to be primary without confirmation by field tests the reversals test should be employed with caution in such sediments as patchy remagnetizations can lead to false polarity stratigraphies

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

early diagenesis in north atlantic abyssal plain sediments characterized by rock magnetic and geochemical indices processes of early diagenesis are investigated in a sequence of late quaternary turbiditic sediments from the madeira abyssal plain map west of the nw african continental margin in three sediment cores from this region solid phase geochemical indices of redox sensitive ion mobilization are compared with rock magnetic parameters as proxies for diagenesis characterization the mud dominated distal turbidites are emplaced mainly as a result of glacio eustatic changes in sea level and derive both from different sites on the nw african margin and from the flanks of the canary islands thus the turbidites are of variable composition especially in terms of carbonate detrital magnetic mineral and organic carbon content within organic rich 0 5 corg turbidite horizons remineralization of organic detritus proceeds in two stages the initial stage involves suboxic reductive diagenesis following depletion of pore water o2 while the later stage involves oxidative diagenesis associated with the slow descent of an oxidation front through the sediment due to diffusion of o2 from the overlying seawater rock magnetic parameters of these sediments when expressed on a carbonate free basis reveal that significant depletion of detrital ferrimagnetic iron fe2 fe3 oxide grains has occurred within the organic rich turbidites during suboxic diagenesis normalized quotients of magnetic parameters and remanence coercivity profiles of selected samples also show that reductive diagenesis is a ferrimagnetic grain size selective process but it has a minimal effect on the canted antiferromagnetic fe3 oxides in the sediment such components if present therefore become relatively enriched in magnetic assemblages as the ferrimagnetic grains are progressively dissolved in all three cores studied however there is clear evidence for the presence of ultrafine ferrimagnetic iron oxide grains at depth within the suboxic zones of organic rich turbidites beneath both active and fossil oxidation fronts these grains are probably associated with populations of live magnetotactic bacteria which inhabit such organic rich horizons and which form a link in the chain of bacterially mediated reactions normally associated with suboxic diagenesis these results comply with previous observations made in studies of suboxic diagenesis in hemipelagic sediments and demonstrate the value of rapid and non destructive rock magnetic measurements for illuminating redoxomorphic processes of diagenesis involving transformation of iron phases in deep sea sediments

rock magnetic properties related to thermal treatment of siderite behavior and interpretation detailed analyses of rock magnetic experiments were conducted on the oxidation products of high purity natural crystalline siderite that were thermally treated in air atmosphere susceptibilities increase sharply between 400 and 530 c indicative of some new ferrimagnetic mineral phase generation both a drop between 540 and 590 c on the heating cycle and a dramatic increase from 590 c to 520 c on the cooling cycle occurred and are well consistent with the characteristic of magnetite a distinct hopkinson type susceptibility peak indicates that hematite is the terminal product if siderite is heated to 700 c over and over it has been revealed in detail that the original inverse magnetic susceptibility fabric contributed by the crystalline anisotropy of siderite in siderite bearing specimens is changed to a normal magnetic fabric during incremental heating over 410 490 c this is a result of dominant contributions from the distribution anisotropy of newly transformed ferromagnetic minerals a strong chemical viscous remanent magnetization could be produced during siderite oxidation in an external field rock magnetic experimental results show that magnetite maghemite and hematite are the transformation products of high temperature oxidation of siderite in air maghemite was not completely inverted to hematite even at temperature as high as 690 c during incremental thermal treatments the mineral transformation processes were confirmed by conventional optical microscopic observation x ray diffractometry and mossbauer spectroscopic analyses these results indicate that the rock magnetic methods used here are reliable and highly sensitive in detecting very small magnetic phase changes in rocks we conclude that these temperaturedependent variations of magnetic properties can be used as criteria for identification of siderite in rocks and sediments furthermore it is clear that great care should be exercised in thermal demagnetization of siderite bearing rocks in paleomagnetic magnetic anisotropy and rock magnetic studies

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

carbon sulfur iron relationships in sedimentary rocks from southwestern taiwan influence of geochemical environment on greigite and pyrrhotite formation the importance of the magnetic iron sulfide minerals greigite fe3s4 and pyrrhotite fe7s8 is often underappreciated in geochemical studies because they are metastable with respect to pyrite fes2 based on magnetic properties and x ray diffraction analysis previous studies have reported widespread occurrences of these magnetic minerals along with magnetite fe3o4 in two thick plio pleistocene marine sedimentary sequences from southwestern taiwan different stratigraphic zones were classified according to the dominant magnetic mineral assemblages greigite pyrrhotite and magnetite dominated zones greigite and pyrrhotite are intimately associated with fine grained sediments whereas magnetite is more abundant in coarse grained sediments we measured total organic carbon toc total sulfur ts total iron fet 1n hcl extractable iron fea and bulk sediment grain size for different stratigraphic zones in order to understand the factors governing the formation and preservation of the two magnetic iron sulfide minerals the studied sediments have low ts fea weight ratios 0 03 0 2 far below that of pyrite 1 15 which indicates that an excess of reactive iron was available for pyritization observed low ts 0 05 0 27 is attributed to the low organic carbon contents toc 0 25 0 55 which resulted from dilution by rapid terrigenous sedimentation the fine grained sediments also have the highest fet and fea values we suggest that under conditions of low organic carbon provision the high iron activity in the fine grained sediments may have removed reduced sulfur so effectively that pyritization was arrested or retarded which in turn favored preservation of the intermediate magnetic iron sulfides the relative abundances of reactive iron and labile organic carbon appear to have controlled the transformation pathway of amorphous fes into greigite or into pyrrhotite compared to pyrrhotite dominated sediments greigite dominated sediments are finer grained and have higher fea but lower ts we suggest that diagenetic environments with higher supply of reactive iron lower supply of labile organic matter and consequently lower sulfide concentration result in relatively high eh conditions which favor formation of greigite relative to pyrrhotite

dung diet and the paleoenvironment of the extinct shrub ox euceratherium collinum on the colorado plateau usa abstract fossil remains of euceratherium collinum extinct shrub ox have been found throughout north america including the grand canyon recent finds from the escalante river basin in southern utah further extend the animal s range into the heart of the colorado plateau e collinum teeth and a metapodial condyle foot bone have been recovered in association with large distinctively shaped dung pellets a morphology similar to a hershey s kiss hk from a late pleistocene dung layer in bechan cave hk dung pellets have also been recovered from other alcoves in the escalante river basin including willow and fortymile canyons detailed analyses of the hk pellets confirmed them to be e collinum and indicate a browser type diet dominated 95 by trees and shrubs artemisia tridentata big sagebrush acacia sp acacia quercus oak and chrysothamnus rabbit brush the retrieval of spring and fall pollen suggests e collinum was a year round resident in the escalante river basin

slope runoff processes and flow generation in a subarctic subalpine catchment hillslope runoff was studied in a subarctic subalpine environment to improve understanding of runoff generation processes and the mechanisms whereby water moves from hillslopes to the stream runoff characteristics of four hillslopes were examined between 1997 and 1999 each with distinct soils frost topography and vegetation lateral fluxes were confined to hillslopes with porous organic soils overlying less permeable mineral substrates setting up a two layer flow system whereby most drainage occurs as quickflow in the porous organic layer as matrix flow and or as preferential flow in pipes rills and interconnected surface depressions during snowmelt meltwater infiltrated and percolated the porous frozen organic layers with little resistance percolation ceased at the organic mineral interface due to the impermeable nature of frozen mineral soils forming a perched saturated zone and initiating runoff snowmelt runoff was greater on slopes with greater snow water equivalent and reduced organic layer thickness in summer runoff was greatest on slopes where wet conditions were sustained by inflow stormflow hydrographs responded rapidly to rainfall while exhibiting extended recessions compared with temperate regions where sustained inflow occurred the recession limb showed two segments to reflect different source areas of stormflow production recession analysis was used to quantify contributing areas which were highly variable and controlled largely by hillslope wetness and organic layer properties results indicate that the concept of variable source area for runoff generation applies to subarctic subalpine catchments

middle and late wisconsin paleobotanic and paleoclimatic records from the southern colorado plateau usa the colorado plateau is a distinct physiographic province in western north america which presently straddles the transition between summer wet and summer dry climatic regimes to the south and northwest respectively in addition to climate the diversity of environments and plant communities on the colorado plateau has resulted from extreme topographic diversity desert lowlands as low as 360 m elevation are surrounded by forested plateaus and even higher peaks greater than 3800 m elevation this environmental diversity provides a unique opportunity to study the history of biotic communities in an arid region of north america although the colorado plateau harbours numerous potential sites the paleoecological record of the plateau is poorly known potential deposits for analysis include packrat middens alluvial and cave sites at lower elevations and lake bog and wetland sites at higher elevations forty six sites have been analysed across the nearly 337 000 km2 region of which 27 contain records that span marine oxygen isotope stage is 2 data with is 3 information coming from only 12 sites most is 2 and 3 sites are clustered along the lowland regions of the colorado river corridor and the uplands of the mogollon rim area we compiled selected data from long paleoecological records to examine patterns of vegetation and climate change across the southern colorado plateau for the middle and late wisconsin during the middle wisconsin mixed conifers covered middle elevations presently dominated by ponderosa pine pinus ponderosa and juniper juniperus woodland grew at elevations today covered by blackbrush coleogyne and sagebrush artemisia desert during the late wisconsin boreal conifers primarily engelmann spruce picea engelmannii replaced the mixed conifer association estimates of mean annual temperatures mat during is 3 were at least 3 4 c cooler than today whereas is 2 mat estimates are at least 5 c colder our investigation of millennial scale climatic variability within the region provided equivocal results the packrat midden sequence could not distinguish vegetation changes that might be associated with heinrich events in the north atlantic from the lake records however many heinrich events were associated with generally drier intervals often with elevated sagebrush pollen concentrations future paleoecological investigations should concentrate on the northern colorado plateau as well as the eastern and western margins additional sites along with closer spaced sampling in regions already studied will be important in determining the history of important climatic phenomena such as the timing of the arizona monsoon

paleoecological and taphonomical aspects of the late miocene vertebrate coprolites urumaco formation of venezuela abstract coprolites fossil feces provide important paleoecological information such as diet of the producer parasite infestation and gut microbiota which cannot be accessed through body remains the upper miocene urumaco formation in western venezuela has a diverse vertebrate fauna composed of ground sloths rodents reptiles fishes and amphibians as well as coprolites here we describe 106 coprolites produced by a range of carnivorous and herbivorous vertebrates classified into five different morphotypes based on their size and shape suggesting different producers herbivorous morphotypes m1 m2 and m5 are the most abundant 59 the most common inclusions in these coprolites are poaceae remains although eudicotyledoneae fragments bacteria and cyanobacteria filaments were also found the m1 morphotype has a bullet shape with longitudinal grooves the m2 morphotype is rounded to oval with at least one distinctive tapered end and the m5 morphotype is a short cylinder with a rough surface and rounded ends in contrast the morphotypes m3 and m4 are attributed by us to carnivores and have different inclusions while m3 is a large cylinder with rounded ends and contains bacteria nematode eggs and phytoliths m4 is sausage shaped and has muscle cells preserved inside based on the co occurring fauna and the morphology of the coprolites the probable producers were inferred as the following m1 a rodent m2 a notoungulate m3 a crocodilian m4 an indeterminate carnivore and m5 a sirenian the preservation of herbivorous and carnivorous coprolites with bacterial parasitological and muscle remains in the same formation and even the same outcrop is rare in the geological record this unique association and preservation suggests early lithification promoted by rapid burial although the presence of the boring trace gastrochaenolites in a single specimen indicates some degree of time averaging

origin of magnetic mineral concentration variation in the southern ocean 1 in the southern ocean magnetic mineral concentration increases in glacial periods the variation pattern closely resembles eolian dust flux records from antarctic ice cores but the cause of the linkage remains unclear as the dust flux is too small for the source of terrigenous materials in the southern ocean we have conducted an environmental magnetic study of late pleistocene sediments from the south indian ocean to investigate the origin of the magnetic concentration changes biogenic magnetites can be detected using the characteristics of almost no magnetostatic interactions and narrow coercivity distribution reflecting occurrence of single domain magnetites in a chain we interpret that a non interacting component on first order reversal curve diagrams and low coercivity components with small dispersion from isothermal remanent magnetization irm component analyses represent biogenic magnetites and that the interacting and middle coercivity components represent terrigenous maghemites the ratio of anhysteretic remanent magnetization susceptibility to saturation irm reflects relative abundance of the biogenic and terrigenous components it was revealed that biogenic magnetites are a dominant constituent of the magnetic minerals in glacials the abundance of both biogenic and terrigenous components increased with increased proportions of the latter increased ocean productivity in glacials is suggested from increased proportions of biogenic magnetites with elongated morphologies indicative of less oxic conditions and increased sedimentation rates these observations suggest that the increased magnetic concentration in glacials in the southern ocean may be explained by iron fertilization the production of biogenic magnetites was enhanced associated with increased ocean productivity which was fueled by increased eolian dust flux

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

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

diagenetic formation of ferrimagnetic iron sulphide minerals in rapidly deposited marine sediments south island new zealand abstract detailed magnetostratigraphic studies of late neogene siliciclastic sediments of the awatere group south island new zealand 41 45 s 174 05 e have revealed a wide range of palaeomagnetic behaviour examination of rock magnetic properties was undertaken using conventional palaeomagnetic techniques and thermomagnetic x ray diffraction and electron microprobe analyses these analyses indicate that the ferrimagnetic iron sulphide minerals greigite and pyrrhotite are responsible for a stable and intense magnetic remanence in fine grained sediments whereas titanomagnetite is the only remanence bearing mineral identified in coarser grained sediments which are less strongly and less stably magnetised than the fine grained sediments detrital titanomagnetite grains are likely to have undergone dissolution during early diagenesis as a result of iron sulphide formation which occurs commonly in rapidly deposited anoxic sediments that support active sulphate reduction and h 2 s formation preservation of greigite and pyrrhotite is inferred to result from the arrest of the pyritisation process probably due to the low permeability of the fine grained sediments and consumption of available h 2 s before full reaction to pyrite occurred relative palaeomagnetic instability and weak remanence intensities in coarser grained sediments is likely to be due to low titanomagnetite concentrations resulting from titanomagnetite dissolution

magnetic properties of pelagic marine carbonates abstract pelagic carbonates are deposited far from continents usually at water depths of 3000 6000 m at rates below 10 cm kyr and are a globally important sediment type recent advances with recognition of widespread preservation of biogenic magnetite the inorganic remains of magnetotactic bacteria have fundamentally changed our understanding of the magnetic properties of pelagic carbonates we review evidence for the magnetic minerals typically preserved in pelagic carbonates the effects of magnetic mineral diagenesis on paleomagnetic and environmental magnetic records of pelagic carbonates and what magnetic properties can tell us about the open ocean environments in which pelagic carbonates are deposited we also discuss briefly late diagenetic remagnetisations recorded by some carbonates despite recent advances in our knowledge of these phenomena much remains undiscovered we are only at early stages of understanding how biogenic magnetite gives rise to paleomagnetic signals in sediments and whether it carries a poorly understood biogeochemical remanent magnetisation recently developed techniques have potential for testing how different magnetotactic bacterial species which produce different magnetite morphologies respond to changing nutrient and oxygenation conditions future work needs to test whether it is possible to develop proxies for ancient nutrient conditions from well calibrated modern magnetotactic bacterial occurrences a tantalizing link between giant magnetofossils and paleogene hyperthermal events needs to be tested much remains to be learned about the relationship between climate and the organisms that biomineralised these large and novel magnetite morphologies rather than being a well worn subject that has been studied for over 60 years the magnetic properties of pelagic carbonates hold many secrets that await discovery

historical reconstruction of organic carbon decay and preservation in sediments on the east china sea shelf 1 sediment cores were collected from the east china sea inner shelf in 2010 to study the decay and preservation of organic carbon oc the highest sediment mass accumulation rate 0 61 0 20 g cm 2 yr 1 derived from 210pb was found near the river mouth and decreased alongshore to the south 0 17 0 004 g cm 2 yr 1 and in an offshore direction 0 31 0 08 g cm 2 yr 1 average total oc content was higher at inner shelf stations 0 52 than those offshore 0 38 the 13c was more depleted at nearshore 23 49 to 21 97 than offshore 22 49 to 21 60 stations principal component analysis indicated that terrestrial oc as indicated by lignin phenols 8 values was preserved in sediment closer to the coast 0 22 0 44 while offshore sediment was more composed of lignin poor 0 12 0 24 degraded oc that was likely hydrodynamically sorted marine derived oc as indicated by plant pigments was significantly more abundant in the sediment mixed layer than the underlying accumulation layer historical flooding events were detected in 8 profiles in two of the six cores located at midshelf stations despite the magnitude of the 2010 flood in east china we did not see any signature of this event with the chemical biomarker in these two cores this may suggest that reduced sediment loading due to recent dam construction may have greatly decoupled river inputs with sediment loading to shelf sediment the total oc standing stock since 1900 was approximately 1 62 1 15 kg c m 2 about one tenth of all the middle and lower lakes in the changjiang catchment basin this work further supports the need for more research to better understand how the reduced inputs of fluvial input of sediments from chinese rivers due to river diversions and dams affect carbon cycling in the east china sea

spatial variability in the abundance composition and age of organic matter in surficial sediments of the east china sea 1 understanding the sources and fate of organic matter om sequestered in continental margin sediments is of importance because the mode and efficiency of om burial impact the carbon cycle and the regulation of atmospheric co2 over long time scales we carried out molecular lignin derived phenols from cuo oxidation elemental isotopic 13c 14c and sedimentological grain size and mineral surface area analyses in order to examine spatial variability in the abundance source age of surface sediments of the east china sea higher terrigenous organic matter values were found in the main accumulating areas of fluvial sediments including the changjiang yangtze estuary and zhejiang fujian coastal zone isotopic and biomarker data suggest that the sedimentary om in the inner shelf region was dominated by aged 14c 423 42 but relatively lignin rich om 0 94 0 57 mg 100 mg oc associated with fine grained sediments suggesting important contributions from soils in contrast samples from the outer shelf while of similar age 14 c 450 99 are lignin poor 0 25 0 14 mg 100 mg oc and associated with coarse grained material regional variation of lignin phenols and om ages indicates that om content is fundamentally controlled by hydrodynamic sorting especially sediment redistribution and winnowing and in situ primary production selective sorption of acid to aldehyde in clay fraction also modified the ratios of lignin phenols the burial of lignin in east china sea is estimated to be relatively efficient possibly as a consequence of terrigenous om recalcitrance and or relatively high sedimentation rates in the changjiang estuary and the adjacent zhejing fujian mud belt

sedimentation dynamics in the east china sea elucidated from and sedimentation dynamics in the east china sea was investigated based on profiles and inventories of 210 pb 137 cs and ex 239 240 pu in sediment cores collected from various settings in this marginal sea the derived sedimentation rates vary by two orders of magnitude from 2 to 0 02 cm yr y1 and generally decrease southward along the inner shelf and eastward offshore this pattern is consistent with the dispersal of yangtze river derived sediments by the current and tidal systems y2 y1 the weighted mean sedimentation rate over the shelf ca 0 3 g cm yr appears to be higher than fluvial inputs from the y2 y1 yangtze river and taiwan 0 14 g cm yr the discrepancy can be reduced by considering the effect of sediment mixing which renders sedimentation rates overestimated and the possibility of additional sediment input from the yellow river s dispersal system spatial variations of the observed nuclide inventories in sediments suggest extensive sediment redistribution boundary scavenging of 210 pb and large inputs of 137 cs and 239 240 pu from yangtze river s drainage basin

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

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

diagenesis of magnetic minerals in recent haemipelagic sediments rapidly deposited sediments from marine and lake environments are being used increasingly to study decadal to millennial fluctuations in the earth s magnetic field the objectives are to gain more fundamental understanding of the geodynamo and to establish a new dating technique for sediments while lacustrine sections are generally restricted to temperate latitude glacial lakes 20 000 yr old rapidly deposited marine sediments along continental margins potentially offer continuous high resolution yet long term records of geomagnetic secular variation however to interpret the sedimentary magnetic record accurately geochemical processes that affect the reliability of the magnetic signal must be understood we now report downcore magnetic profiles from undisturbed kasten cores taken in rapidly deposited laminated sediments from the gulf of california and in bioturbated haemipelagic muds on the oregon continental slope which give apparently reliable directions but show dramatic decreases in the intensities of natural nrm and artificial arm irm remanences with depth downcore porewater and solid sulphur analyses show concave down decreases in porewater sulphate and systematic increases in pyrite and metastable monosulphides the maximum curvature of the sulphide profile occurs directly below the high magnetization zone combined with other compositional and mineralogical analyses these data suggest that due to oxidative decomposition of organic matter magnetites and other iron oxides become progressively reduced and subsequently sulphidized and pyritized with depth iron reduction seems to occur before sulphide formation changes in magnetic stability parameters are consistent with selective dissolution of the finer sized grains causing downcore coarsening of the magnetic fraction

formation and preservation of greigite fe3s4 in sediments from the santa barbara basin implications for paleoenvironmental changes during the past 35 ka diagenetic processes are known to modify sedimentary records but they can also reveal important paleoenvironmental changes here we investigate variations in sedimentary iron diagenesis and depositional environments for the last 35 ka by analyzing the rock magnetic and geochemical properties of two sediment cores collected in the santa barbara basin california in organic rich sediments early diagenesis often leads to partial dissolution of detrital iron oxides and stepwise formation of authigenic pyrite fes2 the pyritization process takes place following several geochemical pathways sometimes involving intermediate iron sulfide species such as greigite fe3s4 sedimentary conditions in the basin appear to have recurrently favored preservation of greigite identified by its magnetic properties and inhibited its complete transformation into pyrite the holocene interval contains a series of centimeter thick greigite bearing layers that are associated with large flood deposits which are known in the basin as gray layers we propose that greigite preservation was enabled in these sediments by their relative enrichment in reactive iron over organic matter and or hydrogen sulfide because of their high ratio of terrigenous over organic material which limited pyritization reactions within the glacial deposits formation and preservation of meter thick greigite layers occurred in terrigenous rich and organic poor sedimentary layers and is proposed to result from a similar diagenetic process to that in the holocene greigite bearing layers dominance of reactive iron over organic matter and or hs the terrigenous enrichments in the glacial greigite bearing layers are probably related to climatic or sea level changes because they occur at times of massive iceberg releases in the north atlantic the so called heinrich events

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

sedimentation on the inner shelf of the east china sea magnetic properties diagenesis and paleoclimate implications abstract high resolution magnetic analysis was performed on the 19 22 m core md06 3040 27 43 3663 n 121 46 8822 e 46 m water depth from the east china sea ecs inner continental shelf which was recovered during the images xiv md155 marco polo 2 cruise of the r v marion dufresne ipev magnetic grains are mainly transported to the inner shelf from erosion on mainland china delivered by the yangtze river nine 14 c ams dates indicate that the core spans about the last 10 4 ka with an average sedimentation rate of nearly 2 mm yr the primary magnetic mineral assemblage of the uppermost sediments contains magnetite with some contributions from hematite and greigite two main stepwise changes are observed in the magnetic mineral content due to post depositional reductive diagenesis the first occurs from the top of the core to 3 5 m and is characterized by reduction of both the magnetite and hematite contents the second occurs at 8 45 9 m and is characterized by a loss of fine grained ferrimagnetic material variations in the magnetic mineral content of this core are related to geochemical and redox environment changes in the ecs through the oxic suboxic sulfidic methanic zones from top to bottom despite significant reduction of a large amount of the ferrimagnetic mineral content due to diagenesis intervals characterized by lower magnetic mineral concentrations and higher coercivities are still identified at 0 45 0 6 1 5 1 7 2 9 3 1 4 4 4 7 5 3 5 7 5 9 6 1 and 8 2 8 4 ka these intervals are in phase within dating errors these intervals are in phase with weak summer monsoon events which indicate that a relationship between magnetic results and paleoclimatic events is partially preserved