magnetic susceptibility as a high resolution correlation tool and as a climatic proxy in paleozoic rocks merits and pitfalls examples from the devonian in belgium low field magnetic susceptibility in measurements are quick and sensitive enabling the creation of high resolution records making in an attractive correlation tool and a proxy for paleoclimate and paleoenvironments in geologically young material foremost in cenozoic sediments in belongs to the geoscientist s toolkit however in is a convolved signal and may reflect other processes than the often implicitly inferred depositional conditions diagenesis remagnetization and low grade metamorphism can potentially obscure the original depositional in signal this aspect is particularly important when interpreting in records from paleozoic rocks here we review data obtained from a large sample collection of middle to upper devonian sections in belgium comparison of in trends with paleoenvironmental indicators facies and with detrital input proxies zr th ti al allowed to assess the persistence of depositional trends furthermore the in signal was deconvolved into its dominant mineralogical contributions with the help of magnetic property analysis the main results are pointing to a magnetic signal dominated by fine grained magnetite of which paleomagnetic analysis indicated a formation during carboniferous remagnetization this prompts a potentially strong influence of post depositional processes and it complicates the interpretation of in records in terms of depositional environments however in most of the sections there is a relatively good relationship between in trends and facies evolution and between in and geochemical proxies for detrital inputs this indicates that the newly formed magnetite grains would at least partly remain where they are formed and this allows a relative preservation of the original signal despite the strong influence of diagenesis two sections show a stronger impact of diagenesis where for about half of these sections the primary depositional information is lost the eifelian givetian monts de baileux section was selected for time series analysis of the in series the average spectral misfit asm method is applied to explicitly evaluate the null hypothesis of no orbital signal and in this section there is 99 05 chance that the ms signal is reflecting an orbital imprint

associations between burial diagenesis of smectite chemical remagnetization and magnetite authigenesis in the vocontian trough se france results of a paleomagnetic rock magnetic geochemical and petrographic study on jurassic and cretaceous carbonates in the vocontian trough support a hypothesized connection between burial diagenetic alteration of smectite and the widespread occurrence of a chemical remanent magnetization crm carried by magnetite where smectite has altered to other clay minerals limestones are characterized by a prefolding secondary normal polarity magnetization throughout the basin the magnetization is interpreted to be a crm based on low burial depths which cannot cause thermoviscous resetting where significant smectite is still present the crm is absent weakly developed and where the clays show no evidence for burial alteration the units are characterized by a primary magnetization crm intensity also varies with the amount of smectite and burial isothermal anhysteretic and natural remanent magnetization intensities increase where smectite has altered both stratigraphically and geographically this is interpreted to indicate magnetite authigenesis associated with clay diagenesis superparamagnetic magnetite is more dominant in highly altered units based on the results of low temperature experiments all sections away from the alps have 87sr 86sr values that are similar to coeval seawater and stable isotopes of carbon and oxygen show no sign of alteration orogenic type fluids therefore are not a likely agent of remagnetization near the alps the rocks are characterized by an additional reversed polarity component which is interpreted to reflect acquisition of the crm through a reversal a postfolding magnetization is also present there and strontium isotopic ratios are higher than elsewhere in the basin and might indicate some alteration by orogenic type fluids we conclude that burial diagenesis of smectite is the likely cause for the development of the widespread crm in the vocontian trough and that this mechanism might explain widespread chemical remagnetization elsewhere

isotopic reconstruction of the african humid period and congo air boundary migration at lake tana ethiopia abstract the african humid period of the early to mid holocene 12 000 5000 years ago had dramatic ecological and societal consequences including the expansion of vegetation and civilization into the green sahara while the humid period itself is well documented throughout northern and equatorial africa mechanisms behind observed regional variability in the timing and magnitude of the humid period remain disputed this paper presents a new hydrogen isotope record from leaf waxes d wax in a 15 000 year sediment core from lake tana ethiopia 12 n 37 e to provide insight into the timing duration and intensity of the african humid period over northeastern africa d wax at lake tana ranges between 80 and 170 with an abrupt transition from d enriched to d depleted waxes between 13 000 11 500 years before present 13 11 5 ka a similarly abrupt transition from d depleted to d enriched waxes occurs ca 8 5 8 ka and is followed by generally d enriched waxes throughout the late holocene trends in d wax covary with changes in northern hemisphere summer insolation and reflect increased precipitation at lake tana during the ahp however the transition from d depleted to d enriched waxes occurs earlier at lake tana ca 8 ka vs 5 ka than in many other regional records and the amplitude of d depletion during the ahp is larger at lake tana as well we attribute this early enrichment to a reduction of moisture derived from westerly sources the congo basin and atlantic ocean which we suggest are d depleted relative to moisture sourced from the east indian ocean and the north red sea and mediterranean sea our new record highlights the importance of both the northward migration of the tropical rain belt as well as east west migration of the congo air boundary to precipitation source and amount during the african humid period

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

late paleozoic remagnetization in limestones of the craven basin northern england and the rock magnetic fingerprint of remagnetized sedimentary carbonates samples of lower carboniferous chatburn and pendleside limestones collected from 27 sites in the craven basin northern england carry a syn hercynian remagnetization residing in magnetite the paleomagnetic directions are all of reversed polarity consistent with a kiaman superchron remagnetization the partially 62 tilt corrected mean direction has the minimum correlation statistic implying a synfolding magnetization the resulting pole appears to be late carboniferous in age and there is no indication of any magnetization component that predates the remagnetization event the magnetization appears to be of the same type as the synfolding remagnetizations documented in several appalachian carbonate units jackson 1990 reported that remagnetized appalachian carbonates have distinctive hysteresis properties and we have obtained similar hysteresis loops from remagnetized paleozoic carbonates from the craven basin england the great basin nevada alaska and new york state the hysteresis loops are all wasp waisted and yield highly anomalous hysteresis ratios compared to data from synthetic or typical magnetite bearing samples in contrast unremagnetized limestones from italy show hysteresis behavior which is more typical for magnetite bearing rocks channell and mccabe this issue these results suggest that remagnetization in magnetite bearing carbonates can be readily detected on the basis of hysteresis properties prior to a full scale paleomagnetic investigation

magnetite authigenesis and diagenetic paleotemperatures across the northern appalachian basin the concentration of magnetite in the lower and middle devonian helderberg and onondaga carbonate formations varies in a distinct pattern along an east west profile across new york state magnetite concentrations are uniformly low in the western half of the profile increase sharply eastward to a peak value near syracuse and decrease farther east the pattern strongly resembles previously reported variations in the extent of clay mineral diagenesis that reflect differences in paleotemperatures along the profile previous paleomagnetic studies have documented that the magnetite carries a well defined magnetization of pennsylvanian permian age and magnetite authigenesis is therefore no younger than late paleozoic we attribute the correlation between high magnetite concentration and high illite content to temperature dependent diagenesis triggered by orogenic fluids the large proportion of secondary magnetite indicates that over most of the area the mechanism of late paleozoic remagnetization was principally chemical thermal effects played a less direct role in the remagnetization of the strata by controlling the extent of the chemical processes that resulted in overprinting of the original remanence

stable isotope records of late quaternary climate and hydrology from mediterranean lakes the isomed synthesis lake isotope records can be used to assess the spatial coherency of late quaternary climate change across the circum mediterranean region we place modern and palaeo data within a simple conceptual lake response model to show that the isotope hydrology of most mediterranean lakes has been influenced strongly by water balance even in those systems that are chemically dilute i e freshwater 18o data on biogenic and endogenic carbonates from 24 lake basins are used to reconstruct multi millennial scale trends since the lgm while it is difficult to make direct comparisons between lake records in terms of single climatic parameters coherent regional isotopic trends can be identified during glacial times mediterranean lakes deposited carbonates isotopically heavier in 18o compared to the holocene partly due to source area effects isotopic enrichment was most marked during intervals corresponding to the h1 and younger dryas events confirming that late pleistocene cold stages in the north atlantic region were marked by aridity around much of the mediterranean almost all mediterranean lake records shifted to more depleted isotopic values during the last glacial interglacial transition lgit this shift is the reverse of the trend which characterised the same transition in lakes from northern and central europe and suggests that temperature changes were not an important direct driver of mediterranean lake isotopic records over glacial interglacial timescales in the early holocene many lakes in the eastern part of the region were more depleted isotopically than in recent millennia this corresponds with marine sapropel formation both chronologically and geographically and implies that increases in local rainfall contributed significantly to the creation of a freshwater lid and anoxia in the east mediterranean sea in contrast no such pattern is currently apparent from lake isotope records from the west mediterranean suggesting a possible nw se contrast in climate history during the holocene

concurrence of folding and remagnetization events in the monterrey salient ne mexico abstract carbonate formations from many locations reveal magnetizations that are secondary attaching a numerical age to these remagnetizations would provide information on orogenic processes to contribute to the effort of assigning an age to remagnetization events lower cretaceous formations from the monterrey salient in northeast mexico were sampled individual fold tests reveal eight site pair synfolding remagnetizations set a of eocene age the remanence is a chemical remanent magnetization crm carried by magnetite the magnetization of set b is possibly due to an early carbonate alteration that produced a remanence significantly older than folding a complexity of set b is that the site pairs reveal k versus unfolding percentage diagrams with maximum unfolding peaks at 100 to 125 an explanation of multiple deformation phases with an earlier horizontal folding phase around a non plunging horizontal axis and a later vertical axis rotation is suggested for the past 100 peaks of the b sites the latter deformation rotation about a vertical axes is revealed by a declination strike test in set a sites and site means of the full collection that deviate counterclockwise from the reference declination by combining synfolding results with published 40ar 39ar illite ages of folding fitz diaz et al 2016 remagnetization ages in set a sites of 48 52 ma are obtained the magnetization in set b sites is likely older though not well constrained interestingly prior results from the central sierra madre oriental to the south show two remagnetization events late cretaceous and early eocene in age in a succession from w to e nemkin et al 2015 the age of folding and remagnetization acquisition in set a sites along the monterrey salient are concurrent with the frontal remagnetized folds in the central sierra madre oriental thus the timing of major remagnetization in the monterrey salient occurred in the eocene

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

remagnetization and orogenic fluids testing the hypothesis in the central appalachians summary palaeomagnetic and geochemical studies on devonian sedimentary rocks in the valley and ridge province in west virginia indicate that the hypothesized relationship between orogenic fluids and remagnetization is not straightforward the helderberg group an aquitard and the oriskany formation a palaeoaquifer both contain similar synfolding late palaeozoic chemical remanent magnetizations crms residing in magnetite the results from the oriskany formation are consistent with remagnetization by orogenic fluids because the unit contains geochemical evidence for the migration of such fluids in contrast there is no geochemical evidence for the widespread migration of orogenic fluids into the helderberg group and thus the crm cannot be related to such fluids another remagnetization mechanism which remains elusive must be responsible for the crm in the helderberg group

rb sr and k ar dating of clay diagenesis in jurassic sandstone oil reservoir north sea rb sr and k ar isotopic determinations were combined with scanning electron microscopy sem observations and x ray diffractometry xrd controls to date the diagenetic formation of clay minerals from oil bearing sandstones of the middle jurassic brent sandstone in the north sea the separated clay fractions often contain detrital components especially k feldspars which are reduced to sizes smaller than 0 4 m either by intense in situ alteration or by destructive sample preparation direct rb sr and k ar isotopic dating of diagenetic illite therefore was not possible isotopic data obtained on mixtures of detrital and newly formed components showed however that illite formed about 40 to 45 ma this value also was obtained directly on clay fractions separated by a gentle method of disaggregation illitization is related to emplacement of hydrocarbons and associated waters into the formation aqueous and hydrocarbon fluids simultaneously trapped in quartz overgrowth inclusions indicate late silicification contemporaneous with this fluid migration minimum trapping temperatures of at least 110 c for these fluid inclusions are too high for the present burial depth hot fluids are assumed to have originated in deep source rocks beneath the brent reservoirs and migrated upward during the middle eocene

replacement of pyrite framboids by magnetite in limestone and implications for palaeomagnetism limestones are an important source of palaeomagnetic data with magnetite the dominant carrier of the magnetization because the magnetite is present in low concentrations however it has been directly observed only rarely and in trace amounts in acid treated separates such residues are composed primarily of spheres the ultimate origin of which has been enigmatic7 yet interpretation of the palaeomagnetic data depends on a knowledge of the origin of the magnetite which has been inferred to carry either a chemical or a viscous remanent magnetization here we present electron microscope data obtained from a sequence of samples of onondaga limestone from an east west traverse across northern new york which unambiguously show that magnetite spheres are derived by alteration and replacement of framboidal pyrite remagnetization is thus caused by chemical rather than viscous processes this chemical remanent magnetization is compatible with a fluid mediated event occurring on a regional scale induced by tectonic stress of alleghenian late palaeozoic age

palaeoecological evidence for holocene environmental change from the virunga volcanoes in the albertine rift central africa abstract this study presents two new well dated sedimentary pollen and charcoal records from high altitude crater sites in the virunga volcanoes located in the albertine rift central africa currently part of one of the world s most biodiverse areas here we argue that holocene vegetation changes in a ca 8000 year palaeoenvironmental record from a crater swamp at an altitude of 3474 m and a ca 2800 year record from a crater lake at an altitude of 4127 m are linked to variations in both climate and human activity climatic changes during the mid to late holocene are reflected in the high altitude sites and more widely in adjacent parts of the albertine rift vegetation changes comprising a decline in ericaceous vegetation at ca 5000 cal yrs bp and subsequent expansion of afroalpine vegetation together with a later increase in taxa associated with lower montane forest particularly podocarpus reflect increasing aridity during the mid to late holocene human induced environmental change in the virunga volcanoes is apparent only within the last millennium despite the long history of human occupation of the area both study sites record significant forest clearance at ca 900 cal yrs bp involving a reduction in lower montane forest taxa and increases in disturbance indicators changes in the composition of upper montane forest and particularly the expansion of hagenia are possibly linked to anthropogenic induced changes in the fire regime and are apparent from ca 900 cal yrs bp human induced environmental modification from the early part of the last millennium likely associated with onset of the late iron age appears to have extended to high altitudes the importance of natural long term climate change as a major cause of environmental change in the albertine rift has been eclipsed within the last millennium by human induced environmental effects

a genetic link between remagnetization and potassic metasomatism in the devonian onondaga formation northern appalachian basin whole rock chemical analyses indicate that the onondaga formation along a rochester syracuse new york transect has a marked eastward increasing trend in k al ratio which correlates with an increase in authigenic magnetite content and degree of diagenetic illitization an eastward increase in the content of some authigenic minerals including k feldspar quartz and fe rich chlorite in the rocks is indicated by petrographic and x ray diffraction studies these observations suggest a link between remagnetization and potassic alteration of fe bearing silicates in the onondaga two hypothetical reactions are proposed in which magnetite authigenesis is related to the breakdown of fe bearing smectite in the presence of potassium products of these reactions include authigenic k feldspar illite quartz and chlorite as well as magnetite our results suggest that remagnetization was triggered by a basin wide migration of k rich fluids during the alleghenian orogeny

evidence for a widespread climatic anomaly at around 9 2 ka before present 1 the 8 2 ka event was triggered by a meltwater pulse mwp into the north atlantic and resultant reduction of the thermohaline circulation thc this event was preceded by a series of at least 14 mwps their impact on early holocene climate has remained almost unknown a set of high quality paleoclimate records from across the northern hemisphere shows evidence for a widespread and significant climatic anomaly at 9 2 ka b p this event has climatic anomaly patterns very similar to the 8 2 ka b p event cooling occurred at high latitudes and midlatitudes and drying took place in the northern tropics and is concurrent with an mwp of considerable volume 8100 km3 as the 9 2 ka mwp occurs at a time of enhanced baseline freshwater flow into the north atlantic this mwp may have been despite its relatively small volume sufficient to weaken thc and to induce the observed climate anomaly pattern

thermoviscous remagnetization in some appalachian limestones experimental evidence shows that blocking temperature relaxation time theory for single domain magnetite can grossly underestimate laboratory thermal demagnetization temperatures of a present day viscous remanence in devonian limestones of new york state thermoviscous remagnetization at moderately elevated burial temperatures during the late paleozoic cannot therefore be readily excluded for the origin of the stable secondary component in these rocks more generally these results emphasize that single domain thermal activation theory cannot be assumed a priori to correctly predict temperature of thermoviscous remanence acquisition in all magnetite bearing rocks the prob leto

remagnetization of carbonate rocks in southern tibet perspectives from rock magnetic and petrographic investigations netherlands organization for scientific research nwo with a rubicon grant 825 15 016 institute for rock magnetism irm at the university of minnesota instruments and facilities program of nsf erc starting grant 306810 nwo vidi 864 11 004

orbital imprint on holocene palaeohydrological variations in west central europe as reflected by lake level changes at cerin jura mountains eastern france this paper presents a lake level record for the holocene at lake cerin jura mountains eastern france it is based on a range of sedimentological techniques validated in previous studies with a combination of systematic lithostratigraphic investigations of the infillings accumulated in the lacustrine basin and sediment analyses of two selected cores the chronology is based on 10 radiocarbon dates and pollen stratigraphy on a millennial scale the cerin lake level record shows three distinct successive phases characterised by higher lake level conditions until ca 9000 cal a bp followed by a maximal lowering at ca 9000 8500 cal a bp and a progressive rise until the present this rise was punctuated by centennial scale fluctuations with major events around 4000 2800 and after 1500 cal a bp considered on a multimillennial scale the general pattern of palaeohydrological changes reconstructed at cerin reflects the impact of orbitally driven summer insolation this is in agreement with other regional and extra regional palaeoclimatic records although every record shows peculiarities in timing and shape depending on the proxy used for reconstruction in this general context centennial to multicentennial oscillations appear to have been second order events in comparison with the major influence of the orbital factor copyright 2011 john wiley sons ltd

direct dating of carbonate remagnetization by 40ar 39ar analysis of the smectite illite transformation abstract the occurrence of remagnetizations in carbonate rocks is a longstanding issue the result of a cryptic process that affects rocks in both fold thrust belts and undisturbed continental interiors this paper examines the clay mineralogy of insoluble material from remagnetized carbonates taken from the cantabrian asturian belt northern spain detailed x ray diffraction patterns indicate that mixed layer clays from these rocks are mostly illitic with an increasing proportion of authigenic illite polytype 1m d in finer grain size fractions the 40 ar 39 ar age data from the different grain size fractions coupled with quantitative polytype modeling indicates an authigenic age that is coeval with the established late paleozoic remagnetization age of these rocks we propose that the transformation of fe rich smectite to fe poor illite created a population of authigenic magnetite that is responsible for the remagnetization of these rocks the irreversible kinetic dependence of clay mineral transformations appears to account for the irreproducibility and unpredictability of carbonate remagnetization and may explain such vexing phenomena as synfolding magnetizations this technique provides an independent assessment of the presence and timing of rock remagnetization with numerous potential applications in future studies of carbonate sequences

effect of submerged breakwater on profile development the project dynamics of beaches is carried out by a network of six european universities within the framework of the human capital and mobility program of the european union the aim of the project is to improve the existing knowledge on physical processes governing the nearshore zone due to effects of submerged breakwaters within the project hydrodynamic and morphological experiments have been carried out this paper discusses the results of the experiments that took place in a wave flume and the large wave basin at delft university of technology the experiments were carried out with movable beds and varying wave conditions

accretion of a rifted passive margin the late paleozoic rhenohercynian fold and thrust belt middle european variscides in the western rhenish massif the rhenohercynian fold and thrust belt of the middle european varsicides exposes a telescoped complete devonian to early carboniferous passive margin this permits the analysis of geometry and kinematic processes of passive margin accretion to an erogenic wedge during variscan collision 330 300 ma the sedimentary cover of the passive margin was shortened by some 50 or 180 km crustal scale balancing and restoration reveals a wide symmetric rift with a central graben a marginal plateau separated this failed lower devonian rift from an emsian middle devonian oceanic basin in the south remnants of which are preserved in the southernmost imbricates and the giessen harz nappes the seismically well imaged aachen midi detachment faille du midi acted as the basal decollement of this thin to thick skinned orogenic wedge it shows a ramp and flat geometry from the blind tip down to middle crustal levels owing to its position below the base of the basin fill the thick synrift sequence and structure controlled structural evolution during contraction by localizing thrust branch lines and by inversion of rift structures synthetic to the subduction direction with formation of basement footwall shortcuts moreover the three dimensional detachment geometry shows large scale oblique ramp flat features which control the architecture of the belt and the distribution of metamorphic grade rocks and fabrics from the detachment show that the latter was located at the transition into the ductile field at the fossil 300 400 c isotherm in the restored section the detachment trajectory displays a saucershaped geometry rising to the surface at the rear and at the front this suggests that the basal detachment propagated into the passive margin by ductile failure during lithospheric flexure under the load of an advancing upper plate the regional pattern of synkinematic metamorphic grade shows varying modes of margin accretion basal underplating into the orogenic wedge by the shelf slope and marginal plateau with formation of duplex stacks and elongate thrust sheets and frontal accretion of the remaining thicker failed rift in the north into the propagating wedge with formation of several imbricate fans cyclical changes in accretion history and or critical taper are suggested by spaced domains of out of sequence thickening these are also related to internal domainal kinematic partitioning of the wedge controlled by oblique collision

time constraints for the tectono thermal evolution of the cantabrian zone in nw spain by illite k ar dating abstract contrasting sedimentary facies and tectonic structures diversely distributed and affected by diagenetic to low grade metamorphic activity form a complex pattern in the northwestern spanish cantabrian area of the variscan orogen the distribution of these metamorphic features is based on field observations clay mineralogy mineral crystallinity indices vitrinite reflectance data and observation of rock microtextures k ar dating of fine grained illite rich size fractions provides a complete set of ages for the episodic deformation and thermal overprints in the southeastern cantabrian area the usual k ar isochron plotting was combined with the bench type age distribution to unravel the successive illite crystallization episodes several tectono thermal episodes occurred in the southeastern pisuerga carrion province initially during the early permian at 293 4 ma in the ruesga line valsurvio dome and sierra del brezo area a further mid permian event was detected at 268 6 ma in the palentine nappes and during the mid triassic at 243 5 ma again in the valsurvio and sierra del brezo areas and along the ruesga line a later reactivation of the ruesga line was detected during mid jurassic time at 175 6 ma

remagnetisation of a rock analogue during experimental triaxial deformation abstract synthetic specimens containing pseudo single domain magnetite were given a univectorial anhysteretic remanent magnetisation they were deformed in a ductile manner at room temperature under a confining pressure of 150 mpa 1 5 kbar the strain rate was 10 5 s 1 and the maximum strain achieved was 23 shortening a weak 0 035 mt magnetic field was present in the pressure vessel during deformation hydrostatic compaction alone produced pressure demagnetisation of low coercivity components of remanence but did not change remanence directions macroscopic differential stress was needed to deform the specimens and this also permitted syndeformational remagnetisation for values of more than 20 mpa 200 bars this added new components of piezo remanent magnetisation prm approximately parallel to the direction of the magnetic field in the pressure vessel they were acquired in all coercivity intervals but the largest components were added below 35 mt the final remanence orientation and its spatial distribution of vector components were dictated by the relative orientations of the remagnetising field and the initial remanence prm contributions almost completely masked the changes related to strain induced grain rotation at these low strains the directions of the externally imposed stress strain axes may not significantly influence the direction of new remanence components prm acquisition occurs when differential stress exceeds a threshold value that probably depends on the previous stress history of the magnetite grains in part this may explain the origin of syntectonic remagnetisation in some naturally deformed rocks where the remanence is not reset by recrystallisation or thermal or chemical processes

identification of remagnetization processes in paleozoic sedimentary rocks of the northeast rhenish massif in germany by k ar dating and ree tracing of authigenic illite and fe oxides 1 this study combines mineralogical chemical rare earth elemental ree and isotopic k ar data of clay minerals as well as chemical compositions major and ree of fe oxide leachates from remagnetized palaeozoic sedimentary rocks from ne rhenish massif in germany for which the causes of remagnetization are not yet clear the dominant carrier of the syntectonic pervasive carboniferous magnetization is magnetite the middle devonian clastic rocks record an illitization event at 348 7 ma probably connected to a major magmatic event in the mid german crystalline rise whereas a second illitization episode at 324 3 ma is coeval to the northward migrating deformation through the rhenish massif being only detected in upper devonian and lower carboniferous rocks the age of that younger illitization is not significantly different from that of the remagnetization which however is not restricted to the upper part of the orogenic belt but affects also the middle devonian strata the ree patterns of the fe enriched leachates support two mineralization episodes with varied oxidation reduction conditions outlined by varied eu and ce anomalies this is not compatible with a unique pervasive migration of orogenic fluids on a regional scale to explain the remagnetization in the studied region while clay diagenesis and remagnetization are time equivalent in upper devonian and lower carboniferous rocks they are not so in middle devonian rocks transformation of smectite into illite cannot therefore account for the growth of associated authigenic magnetite which must have been triggered by a different process since remagnetization and deformation ages are similar the mechanism could relate to local physical conditions such as pressure solution and changing pore fluid pressure due to tectonic stress as well as to chemical conditions such as changing composition of the pore fluids

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

freshwater chlorophycean algae in recent marine sediments of the beaufort laptev and kara seas arctic ocean as indicators of river runoff freshwater chlorophycean algae are characteristic organic walled microfossils in recent coastal and shelf sediments from the beaufort laptev and kara seas arctic ocean the persistent occurrence of the chlorophycean algae pediastrum spp and botryococcus cf braunii in marine palynomorph assemblages is related to the discharge of freshwater and suspended matter from the large siberian and north american rivers into the arctic shelf seas the distribution patterns of these algae in the marine environments reflect the predominant deposition of riverine sediments and organic matter along the salinity gradient from the outer estuaries and prodeltas to the shelf break sedimentary processes overprint the primary distribution of these algae resuspension of sediments by waves and bottom currents may transport sediments in the bottom nepheloid layer along the submarine channels to the shelf break bottom sediments and microfossils may be incorporated into sea ice during freeze up in autumn and winter leading to an export from the shelves into the deep sea the presence of these freshwater algae in sea ice and bottom sediments in the central arctic ocean confirm that transport in sea ice is an important process which leads to a redistribution of shallow water microfossils

synfolding magnetization in the jurassic preuss sandstone wyoming idaho utah thrust belt the jurassic preuss sandstone exposed in five thrust plates of the wyoming idaho utah thrust belt carries directions of remanent magnetization that group most tightly after only partial unfolding field petrographic and rock magnetic evidence indicates that the carrier of this magnetization is detrital low ti titanomagnetite the detrital titanomagnetite was remagnetized at low temperatures 75 150 c probably completely during folding anisotropy of magnetic susceptibility and petrographic observations indicate that the detrital titanomagnetite has been affected by tectonic strain we suggest that low temperature remagnetization of the detrital titanomagnetite was either a viscous partial thermoremanent magnetization the acquisition of which was enhanced by stress or a piezoremanent magnetization that involved stress induced movement of domain walls during intracrystalline strain or was a combination of the two mechanisms stress may promote remagnetization at temperatures much lower than predicted by current theoretical models other mechanisms such as acquisition of chemical remanent magnetization during folding deflection of a prefolding magnetization by internal strain or combination of components of magnetization with different direction cannot account for the geometry of magnetization in the preuss the locus of acquisition of synfolding magnetization in the preuss migrated in conjunction with deformation in the thrust belt a model is presented in which synfolding magnetization was acquired during cooling and folding as strata moved up thrust ramps a lack of reverse polarity directions remains a puzzling feature of the remanence the remanent direction is tentatively interpreted to reflect the predominant polarity state during its acquisition over an extended rather than a discrete time period during folding in late cretaceous and early tertiary periods of predominantly normal polarity

rock magnetic properties of remagnetized palaeozoic clastic and carbonate rocks from the ne rhenish massif germany summary several rock magnetic properties are reported for remagnetized biohermal carbonate rocks platform carbonate rocks and siliciclastic rocks from the ne rhenish massif germany thermal demagnetization of a triaxial isothermal remanent magnetization irm applied at room temperature identifies a variety of magnetic minerals in the sample set magnetite is the predominant magnetic phase and carries a late palaeozoic remagnetization component and can be accompanied by haematite and pyrrhotite as the carrier of remagnetization high haematite contents are characteristic for samples carrying a remagnetization of triassic age zero field heating of remanence acquired at 10 k indicates significant contribution from magnetic material with blocking temperatures between 10 and 100 k the verwey transition at 120 k is much more pronounced in siliciclastic rocks than in carbonate rocks and is presumably related to the presence of detrital multidomain md magnetite samples from biohermal carbonate rocks have hysteresis properties with high m rs m s and h cr h c ratios similar to those from remagnetized carbonate rocks from north america in those lithologies the intensity decrease of a low temperature irm during heating from 10 to 100 k combined with the absence of paramagnetic minerals high hysteresis ratios magnetic viscosity and frequency dependence of susceptibility give strong evidence for the presence of superparamagnetic sp magnetite this supports the hypothesis of a chemical remagnetization event in the ne rhenish massif during the late carboniferous the rock magnetic properties of siliciclastic rocks are characterized by high amounts of paramagnetic material and md magnetite md material obscures the contributions of other material to the bulk magnetic properties completely in most siliciclastic rocks and partly in platform carbonate rocks

high resolution holocene climate and hydrological variability from two major mediterranean deltas nile and rhone high resolution records of sea surface temperatures ssts and terrestrial n alkanes terr alkanes combined with pollen from the same sedimentary sequences were generated to assess variations in the nile river discharge over the holocene these independent proxy records indicate a period of wetter conditions in the nile watershed during the early holocene consistent with insolation driven enhanced monsoon precipitation known as the african humid period ahp the detection of a dry episode around 9200 yr bp in the terr alkane and pollen time series suggests a temporary weakening of the monsoon intensity most probably triggered by extratropical cooling in the north atlantic an interval of c4 grass expansion between 8800 and 8400 yr bp was also evidenced from the terr alkane distribution and confirmed by palynological data ssts of the coastal waters off the nile delta reveal strong fluctuations in the early holocene followed by a slight warming and two pronounced cold intervals around 3500 yr bp and 150

contribution to the genesis of the sedex type mineralizations of the rhenish massif germany implications for future pb zn exploration the meggen orebody and the number of subeconomic sediment hosted mineralizations at plettenberg affeln oberhundem and gunterod eastern rhenish massif are considered to be typical members of the large sedex family i e submarine hydrothermal zn pb orebodies examples such as howards pass canada mcarthur river and broken hill australia and navan ireland formed between the middle proterozoic and carboniferous as a consequence of slow continental extension long term elevated heat flow and basin dewatering enhanced and focused along deeply penetrating synsedimentary fault zones volcanic activity bound to these fractures has no direct genetic relationship to sedex mineralization based on structural and detailed stratigraphic correlation and facies analysis it can be shown that all sedex type mineralizations of the rhenish massif are bound to one and the same synsedimentary fault zone named here the balve oberscheld fault zone which was reactivated during variscan compressional and extensional movements the trend of this tectonic lineament termed menden oberscheld lineament can be even recognized on maps depicting crustal gravity patterns and the configuration of the moho illite crystallinity measurements in devonian shales along profiles crosscutting the lineament evidence increased variscan to early post variscan metamorphism in the fault system which already had promoted the synsedimentary heat flow indications were found that the metalliferous brines escaping into the meggen basin were bound to a synsedimentary fault situated at the western margin of the meggen basin the widespread zn pb ba mineralizations and anomalies in the middle to upper givetian shales in the plettenberg affeln area are likewise bound to horst and graben tectonism along the balve oberscheld fault zone based on data from economic and scientific research in the rhenish massif the application of paleostructural methods for future basemetal exploration is discussed

implications of k ar ages of whole rock and grain size fractions of metapelites and intercalated metatuffs within an anchizonal terrane white mica bearing fractions ranging in grain size from 0 4 m to 6 3 20 m were separated from metapelites and intercalated metatuffs of the eastern rheinisches schiefergebirge frg the stratigraphic age of these rocks is middle devonian eifelian and they contain detrital material of northwestern provenance old red continent probably mainly derived from the caledonian orogen folding in the carboniferous was associated with cleavage formation and an apparently synkinematic anchizonal metamorphism apparent k ar ages of metapelite fractions display a marked positive correlation with grain size illustrating the detrital influence which is diminished with decreasing grain size and increasing metamorphism determined by illite crystallinity contrasting grain morphologies observed by sem enable the interpretation of apparent age grain size relationship for coarse fractions the anticipated lack of detrital mica in metatuffs is confirmed by the fairly consistent apparent k ar ages determined for the coarser than 0 63 m size fractions which date the anchizonal metamorphism at ca 330 ma comparison of metatuff and metapelite apparent ages suggests that the extent of rejuvenation in the latter was largely dependent on grain size rejuvenation was also somewhat controlled by the degree of anchizonal metamorphism as suggested by differences in k ar results of metapelites which were metamorphosed at variable anchizonal conditions fractions 0 63 m from upper anchizonal metapelites record ca 330 ma ages similar to those of the 0 63 20 m sizes in metatuffs together those results confirm the limited applicability of conventional k ar dating on bulk clay fractions 2 m of very low grade anchizonal metamorphic rocks in dating metamorphic events and concomitant cleavage formation

can a primary remanence be retrieved from partially remagnetized eocence volcanic rocks in the nanmulin basin southern tibet to date the india asia collision paleomagnetic dating of the india asia collision hinges on determining the paleogene latitude of the lhasa terrane southern tibet reported latitudes range from 5 n to 30 n however leading to contrasting paleogeographic interpretations here we report new data from the eocene linzizong volcanic rocks in the nanmulin basin which previously yielded data suggesting a low paleolatitude 10 n new zircon u pb dates indicate an age of 52 ma negative fold tests however demonstrate that the isolated characteristic remanent magnetizations with notably varying inclinations are not primary rock magnetic analyses end member modeling of isothermal remanent magnetization acquisition curves and petrographic observations are consistent with variable degrees of posttilting remagnetization due to low temperature alteration of primary magmatic titanomagnetite and the formation of secondary pigmentary hematite that unblock simultaneously previously reported paleomagnetic data from the nanmulin basin implying low paleolatitude should thus not be used to estimate the time and latitude of the india asia collision we show that the paleomagnetic inclinations vary linearly with the contribution of secondary hematite to saturation isothermal remanent magnetization we tentatively propose a new method to recover a primary remanence with inclination of 38 1 35 7 40 5 95 significance and a secondary remanence with inclination of 42 9 41 5 44 4 95 significance the paleolatitude defined by the modeled primary remanence 21 n 19 8 n 23 1 n is consistent with the regional compilation of published results from pristine volcanic rocks and sedimentary rocks of the upper linzizong group corrected for inclination shallowing the start of the tibetan himalaya asia collision was situated at 20 n and took place by 50 ma

paleomagnetic dating of the smectite to illite conversion testing the hypothesis in jurassic sedimentary rocks skye scotland 1 a hypothesized connection between clay diagenesis and magnetite authigenesis is supported by the results of paleomagnetic rock magnetic geochemical and petrographic studies on jurassic sedimentary rock of skye scotland the results have implications for understanding remagnetization mechanisms and for the development of a paleomagnetic method to date clay diagenesis previous diagenetic studies indicate that rock in north skye contains abundant detrital smectite whereas the clays in the same age rock in south skye have altered to illite because of tertiary igneous activity geochemical 87sr 86sr 13c 18o studies confirm that sedimentary rocks in south skye are altered the magnetization in the rocks in north skye is weak and unstable in contrast the rocks in south skye contain a multicomponent magnetization at intermediate temperatures 225 450 c a magnetization with southerly declinations and negative inclinations or its antipodal equivalent is present at higher temperatures 450 580 c a magnetization with northerly declinations and positive inclinations or its antipodal equivalent is removed both magnetizations have directions similar to tertiary igneous rocks on skye rock magnetic studies indicate the presence of pyrrhotite and magnetite the intermediate temperature component resides in pyrrhotite and or magnetite and is interpreted as a thermoviscous remanent magnetization or a thermochemical remanent magnetization related to the heat and or hydrothermal activity associated with the igneous activity the high temperature component resides in magnetite and is a chemical remanent magnetization crm the presence absence test and the timing of acquisition for this crm suggest that magnetite authigenesis is related to the smectite to illite conversion and that clay diagenesis is a viable remagnetization mechanism

u pb data on zircons for the thermal peak of metamorphism in the variscan odenwald germany u pb data are presented for zircons from metamorphic rocks of the crystalline odenwald that comprises part of the mid german crystalline rise the odenwald can be divided into four principal domains with different magmatic and metamorphic histories on the basis of published structural and petrological data and the presented ages in the eastern boll stein odenwald the metasedimentary rocks contain zircons derived from basement rocks that exceed 2 2 ga in age the intrusion of granitic magmas into these metasedimentary rocks took place before or close to the end of the thermal peak of metamorphism at 375 5 ma ago rapid uplift of the bollstein odenwald occurred at about 320 ma bp later than in the bergstrasser odenwald the western bergstrasser odenwald can be subdivided by geochronological petrological and especially structural data into a northern a central and a southern part in the northern part basic magmatism has an age of 362 7 ma the peak of thermal metamorphism in the southernmost odenwald was accompanied by partial melting of metasedimentary rocks and the formation of new zircons with ages between 332 and 342 ma probable peak metamorphic conditions revealed by two samples from the heterogeneous central part occurred at about 336 ma i e in the same time span as in the southernmost part but later than in the bollstein area and the northern odenwald rapid uplift started earlier in the central and southern part and 10 20 ma earlier than in the bollstein odenwald cooling from 500 to 300 c occurred in the northern part in the time interval between the elevation of the other parts of the bergstraesser odenwald and the bollstein odenwald there is no indication for any thermal equilibrium between 2 25 ga and 375 ma recorded in the zircons of both areas

scanning electron microscopy and rock magnetic studies of magnetic carriers in remagnetized early paleozoic carbonates from missouri this study was supported by nsf ear 90 05075 and 92 19616 institute for rock magnetism irm contribution 9303 the irm is funded by the keck foundation the national science foundation and the university of minnesota

remagnetization and chemical alteration of sedimentary rocks remagnetization is a common phenomenon in rocks and developing a greater understanding of its mechanisms has several benefits acquisition of a secondary magnetization is usually tangible evidence of a diagenetic or thermal event which can be dated using palaeomagnetic techniques this is important because the timing of diagenetic and thermal events is commonly difficult to determine remagnetization can also obscure primary magnetizations and a better understanding of remagnetization could improve our ability to uncover primary magnetizations many chemical remagnetization mechanisms have been proposed including those associated with chemical alteration by a number of different fluids e g orogenic weathering mineralizing hydrocarbons and burial diagenetic processes e g clay diagenesis maturation of organic matter this book contains case studies and review articles that focus on remagnetization chemical remagnetization mechanisms and magnetic changes associated with chemical alteration by hydrocarbons

orogenic wedge growth during collision constraints on mechanics of a fossil wedge from its kinematic record rhenohercynian ftb central europe abstract the kinematic evolution of the rhenohercynian fold and thrust belt of the central european variscides can be reconstructed from incremental strain and palaeostress data synkinematic metamorphism geochronology synorogenic sediments and the geometry of shortening this data set allows to infer the mechanical development with respect to the mohr coloumb theory of critically tapered orogenic wedges growth of the rhenohercynian orogenic wedge was kinematically partitioned into a broad orogen normal moving and a narrow obliquely moving domain the ratio of the final widths of these domains varies from 1 6 to 2 3 this low ratio indicates strong basal coupling growth averages are 14 km ma of shortening and a strain rate of 6 10 16 s 1 the mode of mass transfer from lower to upper plate which controlled the accretion geometry and the particle paths evolved in the long term from dominantly basal to frontal accretion this evolution was accompanied by a decrease in taper from precollisional 18 28 to final 5 8 4 6 accretionary subsystems assemble the wedge each is characterised by a sequence of basal to frontal accretion both rooting in a common detachment the development of the subsystems is supported by the observation of stepwise migration of a foreland bulge ponding flysch subbasins these features imply shorter termed ca 2 ma cyclic mass transfer above a high friction detachment with episodes of basal accretion followed by episodes of a quickly forward propagating thrust front transfer of the basal detachment from ductile mid crustal to brittle conditions via a crustal ramp and particle flow across the ramp provoked large scale adjustment of wedge geometry internal wedge thickening is spatially and chronologically related to the formation of the ramp and was supported by surficial erosion of ca 3 kbar for keeping a critical taper three growth stages of the wedge can be reconstructed the high taper of the precollisional stage plots in the tectonically erosive field in a taper stability diagram then taper decreases to 10 after emplacement of a flysch nappe stack during the final stage of contraction an eastern and a western branch develop with geometries fluctuating around a critically stable state the two branches link with differences in large scale wedge architecture bulk contraction and detachment geometry the latter being controlled by the former basin geometry

vegetation fire and climate history of the lesser caucasus a new holocene record from zarishat fen armenia vegetation fire and climate history are investigated in the 10 000 year record of zarishat fen located today in the steppe grasslands of armenia near east pollen based climate quantification provides a reconstruction of seasonal parameters the development of in situ water dependant plants and of forests at lower altitude at 8200 cal a bp echoes the shift from an arid and cold annual precipitation pann 452mm mean temperature of the coldest month mtco 11 1uc early holocene to a more humid and warmer pann 721mm mtco 6 8uc mid late holocene this marks the onset of lower seasonality in particular more effective precipitation brought during late spring by the westerlies paralleling the mediterranean precipitation pattern precipitation in the near east and central asia decreased during the mid late holocene in favour of higher seasonality controlled in winter spring by the siberian high fire history and sedge based fen development record drier phases at approximately 6400 5300 4900 3000 2200 1500 and 400 cal a bp which resemble the precipitation pattern of the south western mediterranean and contrast with the holocene pattern in the south central and south eastern mediterranean regions arid phases in armenia are believed to be related to multi centennial scale variation of westerly activity north atlantic oscillation like copyright 2013 john wiley sons ltd

itcz and enso like pacing of nile delta hydro geomorphology during the holocene abstract the nile valley accommodates the world s longest river and shaped the development of numerous complex societies providing a reliable source of water for farming and linking populations to sub saharan africa and the mediterranean sea its fertile delta lay at the heart of ancient egyptian civilization however little is known of its morpho sedimentary response to basin wide changes in holocene hydrology here we present two well resolved records from the nile delta based on 320 radiocarbon dates to reconstruct the timing and rhythm of catchment scale modifications during the past 8000 years on the orbital timescale we demonstrate that nilotic hydrology and sedimentation have responded to low latitude insolation forcing while on sub millennial timescales many of the major phases of deltaic modification were mediated by climate events linked to el nino southern oscillation type enso variability

diagenetic magnetite carries ancient yet secondary remanence in some paleozoic sedimentary carbonates many sedimentary carbonate rocks carry stable magnetizations that can be shown to reside in magnetite when such magnetizations are observed it is often argued or demonstrated that the magnetite was incorporated into the sediment during deposition however paleomagnetic and rock magnetic studies in conjunction with analyses of magnetic extracts from the helderberg and bonneterre carbonates united states indicate that the magnetite present in these rocks is most likely of diagenetic i e postdepositional origin

temperature and salinity records of the tyrrhenian sea during the last 18 000 years abstract we have used the modern analogue technique to derive sea surface temperature sst records of the last 18 000 years from two well dated deep sea cores recovered in the tyrrhenian sea results show two major cooling events synchronous with the european and north atlantic oldest and younger dryas events a later cooling of lower amplitude is observed between about 8000 and 4500 yr bp tyrrhenian ssts were similar to those of the upper holocene only during the bolling allerod event and at the beginning of the holocene we compared the sst and the planktonic foraminiferal oxygen isotope records to estimate the surface salinity variations our reconstruction shows that salinity decreased in the tyrrhenian sea during the three cold events whereas high ssts correlate with high salinities during most of the last 18 000 years tyrrhenian sea salinity variations were similar to those of the north atlantic ocean near the entrance of the mediterranean sea the salinity gradient between the two basins was thus constant indicating that the western mediterranean circulation pattern and the freshwater budget were not significantly different from the modern one the case was however different during the middle holocene when the strong salinity decrease associated with the sapropel deposit in the eastern mediterranean basin had no equivalent in the north atlantic ocean this peculiar event can only be explained by a local climatic change and an increase of precipitation

the deltaic nature of amazon shelf sedimentation despite the annual discharge of more than a billion tons of sediment by the amazon river the sedimentary environment near the river mouth has little subaerial expression and thus does not meet the classic definition of a delta the river mouth however is not an estuary either these observations raise a major question as to what type of sedimentary environment the amazon river mouth represents seismic stratigraphy has been examined on the continental shelf at the mouth of the amazon river using high frequency 3 5 khz seismic records from about 6 000 km of ship track these records demonstrate three regions 1 the amazon river has built a subaqueous feature which stretches for hundreds of kilometres offshore and alongshore from its mouth the feature is prograding seaward and accreting upward and it contains fine scale stratification typical of classic deltas the feature forming at the mouth of the amazon is a subaqueous delta it differs from classic deltas primarily in its lack of subaerial expression subaqueous deltas such as the amazon represent the general case of a major river entering an energetic oceanic regime

rare earth elemental systematics of mixed layered illite smectite from sedimentary and hydrothermal environments of the western carpathians slovakia abstract mixed layered illite smectite separates of various sizes from bentonites and shales collected in sedimentary and hydrothermal units of the western carpathians were analyzed for their major trace and rare earth elements rees the major elements fairly reflect the changes in the clay mineralogy related to illitization but a lack of correlation between this chemical composition and the ree contents suggests that their incorporation and fractionation by nucleating and growing illite type particles is complex during both burial induced diagenesis and hydrothermal activity during crystal growth of illite type fundamental particles illitization driven by burial related temperature increase does not fractionate the rees incorporated in the mineral structures but it increases their contents suggesting that the bentonite and shale units of the sedimentary sequence act as closed systems the amount of smectite layers in the i s does not relate to the sum of ree or to the la lu ratio in the bentonites and shales of the east slovak basin sedimentary sequence outlining that ree incorporation and fractionation concern s the illite layers not the smectite layers alternatively the hydrothermal system of dolna ves acts as an open system with supply of the rees by external hot fluids so that the ree contents are not determined by the precipitation of illite the mixed layers illite smectite of the shales yield a narrow span of total ree abundances from 17 3 to 36 5 g g compared to those of the associated bentonites from 1 20 to 93 7 g g of the same basin these differences result from varied origins of the original ree carriers the eu anomaly relates to alteration of the authigenic minerals in the sedimentary bentonites acting as a closed system or to the chemistry of the percolating hot fluids in the dolna ves hydrothermal deposit the data also indicate that no detectable zircon apatite monazite or any other ree carrier occurred in the size fractions at least in the finest and if any these minerals had no significant impact on the ree contents and distribution patterns of the varied analyzed size fractions consisting mainly if not exclusively of mixed layered illite smectite

remanence rotation due to rock strain during folding and the stepwise application of the fold test numerical modeling was conducted to determine the effects of simple models of folding strain on prefolding fisherian distributions of magnetization i found that the constant volume simple shear associated with flexural slip flexural flow folding can rotate a prefolding magnetization to have a maximum precision parameter k value at partial unfolding and thus appear to be synfolding in age if the magnetization is treated as a passive line marker this behavior only occurs for steep initial magnetizations the initial homogeneity of the fisherian precision parameters from each limb is degraded by this type of deformation and may be used to detect a strain modified remanence if the magnetization is carried by rigid mechanically active ellipsoidal or spherical particles a maximum k value at partial unfolding will occur for any initial inclination with the special case that rigid spheres will be rotated to cause a maximum k value at 50 unfolding for any initial inclination homogeneity of limb precisions is not affected in this case a discontinuous model of strain during folding in which pressure solution removes material at an axial planar spaced cleavage and causes limb dips steeper than bedding dips could also produce a maximum k value at partial unfolding strain and remanence studies of flexural slip folding in the allentown formation dolomite and the bloomsburg formation red sandstones and mudstones suggest that 1 the rigid grain model may be a more realistic model of magnetic particle behavior during shear strain and 2 about one quarter to one third of the theoretically predicted simple shear strain occurs in these rocks this amount of strain cannot explain the synfolding behavior observed in the allentown formation but could explain the maximum k values at 80 90 unfolding seen in the bloomsburg formation and perhaps other appalachian clastic rocks

characteristics of magnetic carriers responsible for late paleozoic remagnetization in carbonate strata of the mid continent u s a magnetic analysis of carbonate strata of the mid continent region of the united states indicates that the late paleozoic remagnetization already recognized in the appalachians also affects almost the entire mid continent magnetic intensity is regionally variable with more intense magnetizations occurring on intracratonic arches magnetization is carried predominately by magnetite which often occurs in tiny hollow spheroids composed of well formed octahedral microcrysts spheroid chemistry and morphology suggests that the magnetite is authigenic composed of iron extracted from pre existing pyrite or clay the timing of the remagnetization the character of the magnetite and the regional variation in magnetic intensity support the idea that the remagnetization is a diagenetic consequence of tectonically driven brine migration

end member modelling as an aid to diagnose remagnetization a brief review remagnetization of a palaeomagnetic signal is difficult to recognize independently of directional information the situation becomes more complex when remagnetized rocks pass palaeomagnetic field tests for example when the remagnetization of a rock sequence has occurred before folding it is evident that palaeogeographic reconstructions are seriously flawed when actu ally remagnetized rocks are not identified as such here we discuss the merits and pitfalls of so called end member modelling of acquisition curves of the isothermal remanent magnetization irm to recognize remagnetized strata the technique requires no a priori information about the irm acquisition curves the algorithm unmixes a set of irm acquisition curves into a number of invariant curves termed end members and calculates the mixing proportions of the end members for each sample since primary natural remanent magnetization nrm and remag netized nrm are acquired by different processes their signatures can be recognized from subtle differences in the magnetic properties we illustrate the potential of the approach by three case studies one from spain and two from turkey in which the magnetic properties of remagnetized and non remagnetized rocks are evaluated the natural remanent magnetization nrm of a rock is described asremagnetized when itrepresents apalaeomagnetically younger age thanthe sediment age of the rock formation under study remagneti zation interferes with palaeogeographic reconstruc tions asisincreasinglybeingappreciated the late palaeozoic remagnetization event was firmly rec ognized in the appalachians in the usa in the early 1980s e g mccabe et al 1983 see the review of van der voo torsvik 2012 while the implica tionsoflatepalaeozoicremagnetizationineuropean

the age and timing of folding in the central appalachians from paleomagnetic results comparison of the paleomagnetic pole positions of late paleozoic secondary magnetizations with a time averaged reference apparent polar wander path for north america shows that sedimentary rocks within the central appalachians were remagnetized in the later half of the permian between ca 255 and 275 ma ages of remagnetization do not vary for sites distributed along or across strike of the central appalachian fold and thrust belt or across the appalachian plateau in new york nor do they vary with stratigraphic position of the host rocks however the pattern of folding relative to remagnetization across the valley and ridge and great valley in pennsylvania maryland and west virginia shows a distinct temporal variation individual fold tests yield postfolding magnetizations near the hinterland margin of the fold and thrust belt synfolding magnetizations in the central part of the belt and prefolding magnetizations near the foreland because of the similar age of the late paleozoic magnetization we conclude that rocks across the central appalachians were remagnetized in a relatively short period of time as folding and thrusting propagated more slowly toward the foreland we interpret this pattern to indicate that older folds near the hinterland grew prior to remagnetization folds in the central region grew during remagnetization and folds near the foreland grew after remagnetization rapid remagnetization relative to folding is also evident from the physical characteristics and magnetic properties of secondary hematite in remagnetized synfolding folds in such folds rocks were apparently remagnetized during an increment of fold growth in which there was partial and possibly negligible fold limb rotation collectively these results may constrain the mechanism for basinal fluid mobilization during deformation current models for remagnetization involve the migration of chemically active brines into the foreland during tectonism if realistic our results bear on this model by suggesting that brine migration was not directly related to the successive emplacement of individual thrust sheets as has been suggested for other fold and thrust belts

structural analysis clay mineralogy and k ar dating of fault gouges from centovalli line central alps for reconstruction of their recent activity abstract between the cities of domodossola and locarno the complex centovalli line tectonic zone of the central alps outlines deformation phases over a long period of time probably starting 30 ma ago and under variable p t conditions the last deformation phases developed gouge bearing faults with a general e w trend that crosscuts the roots of the alpine canavese zone and the finero ultramafic body kinematic indicators show that the general motion was mainly dextral associated with back thrusting towards the s the on the basis of the k ar ages and with a thermal gradient of 25 30 c km the studied fault zones were located at a depth of 4 7 km if they were active until now as observed in field the exhumation was approximately 2 5 3 0 km for the last 12 ma with a mean velocity of 0 4 mm y comparison with available models on the recent alpine evolution shows that the tectonic activity in the area relates to a continuum of the back thrusting movements of the canavese line and or to several late extensional phases of the rhone simplon line the centovalli val vigezzo zone therefore represents a major tectonic zone of the central western alps resulting from different interacting tectonic events

mid holocene emergence of a low frequency millennial oscillation in western mediterranean climate implications for past dynamics of the north atlantic atmospheric westerlies the nature and tempo of holocene climate variability is examined in the record of forest vegetation from western mediterranean marine core md95 2043 episodes of forest decline occurred at 10 1 9 2 8 3 7 4 5 4 4 5 and 3 7 2 9 cal ka bp and between 1 9 cal ka bp and the top of the record 1 3 cal ka bp wavelet analysis confirms a 900 yr periodicity prior to and during the early holocene and the dominance of a 1750 yr periodicity after 6 cal ka bp the 900 yr periodicity has counterparts in numerous north atlantic and northern hemisphere palaeoclimate records and in solar irradiance proxies 14c and 10be and may relate to a sun climate connection during the early holocene comparisons between the md95 2043 forest record and strategically located records from morocco iceland norway and israel suggest that the 1750 yr mid to late holocene oscillation reflects shifts between a prevailing strong and weak state of the zonal flow with impacts similar to the positive and negative modes of th

abrupt climate change sea surface salinity and paleoproductivity in the western mediterranean sea gulf of lion during the last 28 kyr abstract the planktonic foraminiferal record of core md99 2346 gulf of lion shows a decrease of sea surface temperature sst at the time of heinrich event h2 24 23 5 cal kyr bp younger dryas and during the early to middle holocene these events were associated with a decrease of surface water salinity the salinity lowering events were similar and synchronous to those recorded in the north atlantic ocean during h1 h2 and the younger dryas they can be explained by a decrease in the salinity of the atlantic surface water entering the mediterranean through the strait of gibraltar this result indicates that the mediterranean sea remained a concentration basin and that its freshwater budget was not significantly different from the modern conditions at the time of these low salinity events higher abundances of the benthic foraminifer cibicidoides pachydermus at the time of heinrich events h2 and h1 may result from a seasonal and more pulsed supply of labile organic matter a high abundance of intermediate and deep infaunal taxa globobulimina spp during the warm bolling allerod period is interpreted as a result of an increased lateral advection of organic matter to the deeper environments of the gulf of lion surface water productivity as reflected by the organic flux to the benthic ecosystem reaches a maximum during the cold younger dryas period it is possible that cold conditions at the time of the younger dryas have allowed an enhanced vertical mixing and deep water cascading in the gulf of lion this may have resulted in an increase of primary and export production this putative intensification of deep water cascading would have occurred after the sustained rise of the global sea level from 16 to 12 5 cal kyr bp the deglacial sea level rise may also have played an important role in favouring the downslope movement of dense shelf water enriched in organic matter originating from the early rhone delta complex the conditions during the holocene were characterized by a low surface productivity and oligotrophic environment similar to the modern situation

palaeomagnetic investigations in the hercynian mountain belt of central europe abstract the palaeomagnetism of sediments and volcanics of middle devonian to early carboniferous age has been studied in the hercynian realm of the vosges harz and franconian forest france and germany after appropriate cleaning characteristic directions of natural remanent magnetization nrm have been determined which are considered to be of pretectonic origin according to rock magnetic and structural geological evidence a mean palaeopole for the devonian rocks in the areas investigated was determined at 29 7 n and 9 0 e the site latitude derived from the devonian rocks agrees very well with that observed in great britain and britanny the significant difference in longitude between our devonian poles and the other european data may be due to an anticlockwise rotation of central europe with respect to the northern hercynian foreland the carboniferous rocks yield a mean palaeopole at 41 7 n and 340 4 e matching the carboniferous part of the european polar wander path a fold test within carboniferous greywackes from the harz mountains proves a pre folding origin of the nrm of these rocks however this stable magnetization direction indicates local or regional tectonic displacement our results do not support any major latitudinal motions of continental segments in central europe during the hercynian orogeny the palaeozoic palaeomagnetic data from the vosges franconian forest harz britanny and central massif can be used to interpret the hercynides in terms of a large scale shear belt

timing of fault reactivation in the upper crust of the st lawrence rift system canada by k ar dating of illite rich fault rocks11geotop contribution 2012 0002 formed during late proterozoic early paleozoic the st lawrence rift system of eastern north america hosts an active seismic zone also displaying evidence of subsequent tectonic reactivation in paleozoic and mesozoic times however lack of a detailed reconstruction of the basement geometry and limited geochronological constraints limit our understanding of its structural evolution late silurian early devonian fault reactivation is demonstrated here in typical fault sites of the st lawrence rift system by combining structural observations of basement structures and a mineralogical morphological and k ar isotopic study of clay rich fault material 0 4 m et 1 2 m the k ar data of clay rich size fractions from gouges of varied rock types from saint laurent and montmorency faults define two isochron ages at 436 45 and 406 22 ma that are within analytical uncertainty and give an average at 421 15 ma however these two faulting episodes could also picture a single long lasting phase of for

holocene climate variability and cultural evolution in the near east from the dead sea sedimentary record abstract a comprehensive record of lake level changes in the dead sea has been reconstructed using multiple well dated sediment cores recovered from the dead sea shore interpreting the lake level changes as monitors of precipitation in the dead sea drainage area and the regional eastern mediterranean palaeoclimate we document the presence of two major wet phases 10 8 6 and 5 6 3 5 cal kyr bp and multiple abrupt arid events during the holocene the arid events in the holocene dead sea appear to coincide with major breaks in the near east cultural evolution at 8 6 8 2 4 2 3 5 cal kyr bp wetter periods are marked by the enlargement of smaller settlements and growth of farming communities in desert regions suggesting a parallelism between climate and near east cultural development

origin of magnetite responsible for remagnetization of early paleozoic limestones of new york state scanning electron microscope and scanning transmission electron microscope observations of thin sections and separates of the devonian onondaga and helderberg limestones and ordovician trenton limestone in new york state allow us to identify three types of magnetite pseudoframboids nonspherical magnetite and fine grained magnetite magnetite was observed replacing pyrite occurring as crystals in spherical pseudoframboids or with nonspherical shapes fine grained magnetite consisting of aggregates of one or more rounded single crystals approximately 2000 a 200 run in diameter could not be observed in thin sections of new york carbonates due to its small size but was found in magnetic extracts hysteresis measurements of magnetic extracts verify that fine grained magnetite is capable of carrying remanent magnetizations however pseudoframboidal magnetite and nonspherical magnetite are polycrystalline and consist of assemblages of single to pseudosingle domain sized crystals that also can be carriers of the remagnetization these data in combination with observations from other localities collectively imply that the alleghenian remagnetization is carried by the fine grained magnetite although pseudoframboidal and nonspherical magnetite may also contribute thus the alleghenian remagnetization is a chemical remanent magnetization due to authigenic magnetite crystallization of magnetite was mediated by fluids with dissolution and crystallization activated by stress during the alleghenian orogeny the origin of such fluids is unknown but they may have originated through crustal scale fluid migration tectonically induced brine migration due to emplacement of thrust sheets is preferred over a meteoric source of the fluids

reconstruction of postglacial to early holocene vegetation history in terrestrial central europe via cuticular lipid biomarkers and pollen records from lake sediments high resolution environmental reconstruction for central european terrestrial settings is commonly based on sediment records that provide the pollen spectra used for reconstruction of vegetation development alternatively complementary algal insect or zooplankton assemblages and or carbonate 18 o isotope profiles are investigated in this study vegetation development and inferred climate evolution were documented on a decadal to centennial scale by analysis of land plant cuticular lipids accumulated in lake sediments wax lipids derived from land plant leaves and blades are source diagnostic and highly resistant to degradation their aerodynamic properties favor short distance eolian transport but they are less affected by possible long distance transportation that complicates pollen analysis the late glacial to holocene sedimentary record of lake steisslingen southwestern germany was investigated by palynological and geochemical means tundra type pioneer vegetation consisting predominantly of grasses and herbs is dominated by nc31 alkanes whereas pioneer birch forest yields preferentially nc27 alkanes establishment of a pine assemblage is recognizable by elevated nc29 and nc31 leaf wax alkanes and the diversification of deciduous forests in the holocene is marked by nc29 dominance lipid geochemistry and palynology resolve decadal excursions such as the mid younger dryas event centennial climate trends with pronounced and rapid changes at the oldest dryas bolling allerod younger dryas and younger dryas preboreal transitions are consistently reflected by molecular and palynological proxy data the demonstrated suitability of an independent molecular proxy in paleoenvironmental studies provides new perspectives in high resolution climate reconstruction

impacts of the north atlantic gyre circulation on holocene climate off northwest africa we present well dated high resolution holocene records of sea surface temperature sst and upwelling intensity off northwest nw africa we identify long term cooling trends over the holocene in the subtropical north atlantic in response to boreal summer insolation a pronounced cooling event of similar to 1 degrees c ca 8 5 cal ka indicates a large scale reorganization of the ocean current system possibly induced by meltwater from the northern north atlantic our alkenone sst record off cape ghir provides strong evidence for the impact of ocean circulation changes on subtropical north atlantic ssts it is likely that cold waters were propagated to the subtropics via the canary current in a way similar to heinrich events and the younger dryas off cape blanc we find 2 3 k y periodic variations in sst and upwelling intensity off nw africa superimposed on the cooling trend such a cycle has been documented in various paleoclimate archives in phase with solar forcing we show that these variations on millennial time scales are linked to the north atlantic subtropical gyre circulation and the northern hemisphere atmospheric circulation and in particular to changes in the pressure gradient between the icelandic low and the azores high this suggests that oceanic circulation in response to solar forcing played a more important role in the generation of 2 3 k y cyclicity than has been previously considered

landscape evolution and geodynamic controls in the gulf of cadiz huelva coast sw spain during the late quaternary abstract the coastal evolution of the el abalario area huelva southern spain during the late pleistocene and holocene is reinterpreted after a refinement of the available geochronology by means of optically stimulated luminescence osl dating new data come from the analysis of soft sediment deformation palaeosols geomorphological mapping and published seismic surveys on the onshore and offshore gulf of cadiz the present structure of el abalario dome resulted from the complex interaction of littoral catchment processes and sea level changes upon an emergent coastal plain conditioned by the upwarping of the underlying pliocene pleistocene prograding deltaic sequence upwarping is probably related to escape of over pressurized fluids accompanied by dewatering prior to and during ois oxygen isotopic stage 5 continued upwarping produced the large nw se gravitational fault of torre del loro tlf in the southwestern flank of the dome roughly parallel to the present coastline during ois 5 ois 4 the resulting escarpment favoured the accumulation of aeolian sand dunes units u1 u2 and u3 from ois 5 to early ois 1 unit u1 ois 5 ends upwards in a supersurface with a thick weathering profile that suggests moist and temperate climatic conditions unit u2 accumulated mainly during ois 4 and ois 3 with prevailing w e winds the supersurface between u2 and u3 records a part of ois 2 with relative low sea level sedimentation of unit u3 took place during the last deglaciation radiocarbon and osl ages with prevailing w sw winds under a temperate moist climate that became more arid towards the top holocene a major supersurface with an iron crust like layer ssfe developed during the holocene climatic optimum ois 1 under wetter and more temperate conditions than before fossilizing the tlf the supersurface is covered by younger aeolian dunes u4 u5 u6 and u7 transported by w sw winds since the late neolithic chalcolithic cultural period 5 0 ky cal bp

millennial scale sea surface temperature changes in the eastern mediterranean nile river delta region over the last 27 000 years 1 in this study we utilize two organic geochemical proxies the u37k index and tex86 to examine past sea surface temperatures sst from a site located near the nile river delta in the eastern mediterranean em sea the u37k and tex86 records generally are in agreement and indicate sst ranges of 14 c 26 c and 14 c 28 c respectively during the last 27 cal ka during the holocene tex86 based sst estimates are usually higher than u37k based sst estimates which is likely due to seasonal differences between the timing of the haptophyte and crenarchaeota blooms in the em and is related to the onset of the modern flow regime of the nile river both records show that sst varied on centennial to millennial timescales in response to global climate events i e cooling during the last glacial maximum lgm heinrich event 1 h1 and the younger dryas yd and warming during the bolling allerod and in the early holocene during deposition of sapropel s1 the h1 cooling was particularly severe and is marked by a drop in sst of 4 5 c in comparison to pre h1 sst with temperatures 1 c cooler than during the lgm in contrast to high latitude and western mediterranean records which indicate both an abrupt onset and termination of the yd event the transition from the yd to the holocene was much more gradual in the em

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

are magnetite spherules capable of carrying stable magnetizations to determine if magnetite spherules extracted from ancient carbonate rocks can carry ancient remanent magnetizations electron microscope observations and magnetic data have been obtained for more than 100 individual spherules extracted from the jurassic twin creek limestone wyoming and the mississippian leadville limestone colorado two categories of surface textures smooth and patterned correlate with different hysteresis parameters spherules with patterned surfaces group a have ratios of saturation remanent magnetization to saturation magnetization msr ms 3 most spherules with smooth surfaces group b have 0 1 msr ms 0 3 and hcr hc 3 the patterned surfaces consist of 1 parallel dendritic nets with units 1 m wide 2 platelets with widths of 1 to 3 m 3 mosaic surface units with diameters between 2 and 5 m each of these surface elements consists of a single crystal as verified by selected area electron diffraction patterns showing sharp spots whereas the spherules as a whole show multicrystalline patterns by x ray diffraction the msr ms and hc values of group a increase with decrease in grain size these group a magnetite spherules are undoubtedly multi domain in character and are unlikely to carry stable ancient remanences the smooth surfaced group b spherules are not very abundant 8 of the entire population and have pseudo single domain psd or multi domain md magnetic properties they may carry ancient remanences although we infer that single domain sd non spherical submicrometer magnetite is the principal carrier of remanence in most carbonates