large scale responses of complex shaped coastlines to local shoreline stabilization and climate change 1 when modeling the large scale km evolution of coastline morphology the influence of natural forces is not the only consideration ongoing direct human manipulations can substantially drive geomorphic change in this paper we couple a human component to a numerical model of large scale coastline evolution incorporating beach nourishment periodically placing sand on the beach also called beach replenishment or beach fill beach nourishment is the most prevalent means humans employ to alter the natural shoreline system in our case study the carolina coastline beach nourishment can cause shorelines adjacent to those that are nourished to shift both seaward and landward when we further consider how changes to storm behaviors could change wave climates the magnitude of morphological change induced by beach nourishment can rival that expected from sea level rise and affect the coast as far as tens of kilometers away from the nourishment site in some instances nonlocal processes governing large scale cuspate cape coastline evolution may transmit the human morphological signal over surprisingly large hundreds of kilometer distances

lithosphere of indus block in the northwest indian subcontinent through genetic algorithm inversion of surface wave dispersion the indus block in the northwest indian subcontinent is a continental area lying between the chaman fault in the west the aravalli range in the east and the main boundary fault of himalaya in the north we evaluate the lithospheric structure of this crustal block through inversion of love and rayleigh wave group velocities obtained using broadband records at bhuj from the kashmir earthquake of 8 october 2005 and its aftershocks the recording station lies in the southern edge and epicenters lie in the northern edge of this block the wave paths are mostly in the study area in a direction parallel to the aravalli trend the period of the group velocity data ranges from 5 4 to 74 1 sec and the inversion of these data resolves the structure down to the lithosphere asthenosphere boundary lab a nonlinear inversion has been carried out through a genetic algorithm with a wide solution space some new concepts of solution space of a layered structure and of a misfit function are used the mean and standard deviation of the 50 accepted solutions with low misfit give the structure ib11 for the indus block the standard deviation gives the estimation of the uncertainty and the resolution of the corresponding parameter in ib11 the sedimentary thickness is 5 6 km within two layers the total thickness of the crust is 44 2 km the s wave velocity below the crust is 4 393 km sec while this velocity is 4 603 km sec in the indian region to the east of the aravalli range in ib11 the lab is at a depth of 79 km which is much shallower than the corresponding depth of 120 km in the indian region on the other hand the s wave velocities below the crust as well as the depth of the lab are similar to those of the arabian shield these similarities support the hypothesis that the indus block is a detachment of the arabian nubian shield

high angle wave instability and emergent shoreline shapes 2 wave climate analysis and comparisons to nature 1 recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms including capes flying spits and alongshore sand waves this instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle a maximum that occurs between 35 and 50 for several common alongshore sediment transport formulae here we introduce metrics that sum over records of wave data to quantify the long term stability of wave climates and to investigate how wave climates change along a coast for long point a flying spit on the north shore of lake erie canada wave climate metrics suggest that unstable waves have shaped the spit and furthermore that smaller scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable a shoreline aligned along the trend of the carolina capes united states would be dominated by high angle waves numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast local wave climates along these simulated capes and the carolina capes show similar trends shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability

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

comparison of magnetic hysteresis parameters of unremagnetized and remagnetized limestones for white magnetite bearing mesozoic pelagic limestones from italy which carry a primary magnetization the values of mrs ms and hcr hc generally lie in the pseudo single domain psd field of the day et al 1977 plot the logarithmic plot of mrs ms against hcr hc gives a straight line r 0 814 with slope and intercept close to the empirical mixing line of parry 1982 for single domain sd and multidomain md magnetite for one of the white pelagic limestone formations maiolica formation samples with hysteresis ratios closer to the md field display increased paramagnetic susceptibility and are from the upper part of the formation characterized by increased detrital clay we therefore associate the increased md magnetite with increased detrital influx for pinkish and reddish varieties of the italian pelagic limestones the presence of hematite is manifest by high saturation fields a wide range of hcr hc and wasp waisted hysteresis loops attributed to the mixing of magnetite and high coercivity authigenic hematite the hysteresis ratios for a collection of paleozoic and mesozoic remagnetized magnetite bearing limestones from britain nevada alaska and the appalachians lie mainly outside the psd field and appear to follow a power law trend following jackson et al 1993 the high values of hcr hc and the characteristically wasp waisted hysteresis loops can be interpreted in terms of a fine grained subspherical high coercivity sd magnetite mixed with a high proportion of superparamagnetic magnetite the slope and intercept of the power law relationship for mrs ms and hcr hc in the remagnetized limestones are distinct from those observed for the italian limestones and may provide a means of fingerprinting magnetite of primary as opposed to diagenetic origin

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

formation of coastline features by large scale instabilities induced by high angle waves along shore sediment transport that is driven by waves is generally assumed to smooth a coastline this assumption is valid for small angles between the wave crest lines and the shore as has been demonstrated in shoreline models but when the angle between the waves and the shoreline is sufficiently large small perturbations to a straight shoreline will grow here we use a numerical model to investigate the implications of this instability mechanism for large scale morphology over long timescales our simulations show growth of coastline perturbations that interact with each other to produce large scale features that resemble various kinds of natural landforms including the capes and cuspate forelands observed along the carolina coast of southeastern north america wind and wave data from this area support our hypothesis that such an instability mechanism could be responsible for the formation of shoreline features at spatial scales up to hundreds of kilometres and temporal scales up to millennia

the fold test in palaeomagnetism summary the fold test suggested by mcelhinny is shown to be inappropriate more correctly one should determine whether the mean direction of a group of sites from one limb of a fold may be distinguished statistically from the mean direction of a group of sites from another limb details of the application of this test are given with examples it is shown that the test indicates significance under far less severe folding than does the test suggested by mcelhinny

large scale dynamics of sandy coastlines diffusivity and instability 1 the dynamics of small amplitude perturbations of an otherwise rectilinear coastline due to the wave driven alongshore sediment transport is examined at large time and length scales years and kilometers a linear stability analysis is performed by using an extended one line shoreline model with two main improvements 1 the curvature of the coastline features is accounted for and 2 the coastline features are assumed to extend offshore as a bathymetric perturbation up to a finite distance for high incidence angles instability is found in accordance with ashton et al 2001 however it is seen that instability is inhibited by high waves with long periods and gently sloping shorefaces so that in this case the coastline may be stable for any angle similarly there is no instability if the bathymetric perturbation is confined very close to the coast it is found that the traditional linearized one line model larson et al 1987 tends to overpredict the coastline diffusivity the overprediction is small for the conditions leading to a stable coastline and for moderate incidence angles but can be very dramatic for the conditions favoring instability an interesting finding is that high angle waves instability has a dominant wavelength at the linear regime which is in the order of 4 15 km one to two orders of magnitude larger than the length scale of surf zone rhythmic features intriguingly this is roughly the same range of the wavelength of some observed shoreline sand waves and in particular those observed along the dutch coast a model application to this coast is presented

observation and inversion of surface wave group velocities across central india abstract surface wave group velocities across central india are measured from computer plots of frequency time analysis using multiple filter technique periods range from 5 to 56 sec for fundamental mode rayleigh wave 5 to 16 sec for first higher mode rayleigh wave and 5 to 49 sec for fundamental mode love wave the wave paths from koyna earthquakes to bokaro cross purely through the peninsular plateau the group velocities for these paths are found to be similar to those of surface waves recorded at poona from earthquake which lie to the northeast of bokaro in sub himalayan regions from this it is concluded that the shield structure of the peninsula extends to the sub himalayan regions to northeast of the peninsular plateu with a negligible part of sedimentary layer group velocities of fundamental mode rayleigh and love waves are also obtained for the paths from koyna earthquakes to shillong and are found to be similar to the above mentioned group velocities except at very low periods where group velocities are affected by the small part of each path through thick sedimentary layer of bengal basin northern limit of this basin sedimentary layer has been identified mean and standard deviation of observed group velocity at each period are obtained for each of rayleigh fundamental rayleigh first higher and love fundamental modes the group velocities closely agree with those obtained earlier for the path between new delhi and kodaikanal and are also found to be similar to those observed in some shield regions monte carlo inversion method is applied and crust and upper mantle structure of the indian shield across central india is obtained crustal structure obtained shows a marked resemblance to the results obtained earlier through body wave study

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

magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies a review of magnetic methods and challenges abstract magnetic iron oxide minerals principally magnetite maghemite hematite and goethite are formed in well drained soils in response to a suite of physical chemical and biological factors despite a wide range of complexity in the pedogenic processes that lead to magnetic mineral formation dissolution and transformation there are well documented empirical relationships between various magnetic mineral assemblages in soils with environmental and climatic conditions recently there has been an increase in the number of quantitative magnetic paleoprecipitation proxies that have been developed and there is great potential for magnetic methods to be used in the geologic record to develop reconstructions of past climates magnetic paleoprecipitation proxies have been widely utilized in quaternary or younger loess paleosol systems however they have yet to be utilized in the pre quaternary fossil record future studies of magnetic mineralogy of soils and paleosols should aim to explore non loessic modern soils and pre quaternary paleosols with more focus on understanding the interaction between magnetic mineral assemblages and soil moisture applications of existing and novel magnetic paleoprecipitation proxies in the fossil record should prove to be a valuable resource for paleoclimatologists

high angle wave instability and emergent shoreline shapes 1 modeling of sand waves flying spits and capes 1 contrary to traditional findings the deepwater angle of wave approach strongly affects plan view coastal evolution giving rise to an antidiffusional high wave angle instability for sufficiently oblique deepwater waves with angles between wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport 45 a one contour line numerical model shows that a predominance of high angle waves can cause a shoreline to self organize into regular quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers the numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash which is assumed to maintain a minimum barrier width systematic analysis shows that the wave climate determines the form of coastal response for nearly symmetric wave climates small net alongshore sediment transport cuspate coasts develop that exhibit increasing relative cross shore amplitude and pointier tips as the proportion of high angle waves is increased for asymmetrical wave climates shoreline features migrate in the downdrift direction either as subtle alongshore sand waves or as offshore extending flying spits depending on the proportion of high angle waves numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude a rate that is insensitive to the proportion of high angle waves the proportion of high angle waves determines the offshore versus alongshore aspect ratio of self organized shoreline undulations

the magnetization of clay rich rocks in sedimentary basins low temperature experimental formation of magnetic carriers in natural samples abstract rocks are often magnetically altered during burial thus providing a useful method to study their thermo chemical history in order to improve the understanding of burial diagenetic magnetization we experimentally synthesized magnetite in natural samples lower jurassic argillites from the paris basin were heated to 150 c under a confined atmosphere of argon when a magnetic field was applied during the heating a chemical remanent magnetization was acquired rock magnetism studies reveal that most of the newly formed magnetic carriers were magnetite using anhysteretic remanent magnetization as a measure of the quantity of magnetite an increase of up to 150 after heating was observed ferrimagnetic iron sulphide and hematite are observed to have formed in samples composed of less than 3 calcite and new magnetite is sometimes completely absent in samples containing less than 0 5 calcite hysteresis measurements suggest that the new magnetite is in the pseudo single domain state scanning electron microscope studies indicate that the new magnetic carriers are associated with pre existing pyrite the magnetic transformations during the experiments involved a fluid which reacted with iron bearing and sulfur bearing minerals in ways depending on local redox conditions this study shows that magnetite can be produced in argillaceous sediments at the normal temperatures and pressures found in sedimentary basins without any external supply from long range fluid flow

separating multidomain and single domain like remanences in pseudo single domain magnetites 215 540 nm by low temperature demagnetization it has long been hypothesized that the pseudo single domain properties of submicron magnetites are a result of coexisting multidomain and single domain like remanences we have separated these two types of remanence by low temperature demagnetization ltd in which samples are cooled through the low temperature magnetite isotropic point and rewarmed to room temperature all in zero field at the isotropic point the first crystalline anisotropy constant vanishes and multidomain remanence due to displaced domain walls will be unpinned we measured stepwise alternating field af and thermal demagnetization curves of weak field thermoremanent magnetization trm and anhysteretic remanent magnetization and of saturation isothermal remanent magnetization irms both with and without prior ltd for magnetites with mean particle sizes of 215 390 and 540 nm the memory fraction of remanence recovered after ltd which represents the single domain like component decreased from 44 for 215 nm grains to 23 for 540 nm grains in the case of irms memory of trm was approximately twice as large af decay curves were soft and multidomain like before ltd but became harder and single domain like in shape after ltd ltd removed most low unblocking temperature trm and irms distributed low unblocking temperatures are therefore a multidomain phenomenon probably resulting from successive adjustments of domain walls to changing internal fields and pinning strengths during heating

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

shield like lithosphere of the lower indus basin evaluated from observations of surface wave dispersion abstract the lithospheric velocity structure of the lower indus basin has been evaluated through inversion of fundamental modes of both love and rayleigh wave group velocities from the broadband records of a seismic network maintained by the institute of seismological research gujarat india we have considered three clusters of wave paths a b and c that mainly cross the lower indus basin from south to north the wave paths of a mainly cross the continental shelf and the wave paths of b and c pass through the lower indus basin the measured group velocities correspond to periods of 5 to 90 s for rayleigh waves and 5 to 115 s for love waves these data sets resolve the structure of the lithosphere through a nonlinear inversion based on a genetic algorithm with a wide solution space the mean and standard deviation s d of the 70 accepted solutions for each of these three clusters provide the 2d structure for the lower indus basin from south to north the sediment consists of two layers with total thickness from 5 7 to 6 6 km increasing northward the crustal thickness also increases northward from 32 9 cluster a to 39 7 km cluster c in the lower indus region the s wave velocity below the crust varies from 4 55 to 4 59 km s which is close to the corresponding velocity of 4 60 km s of the indian shield region to the east of the aravalli range the thicknesses of the lithosphere as well as the velocities of the uppermost mantle of the lower indus plain are similar to that of the indian shield

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

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

diagenetic sources of stable remanence in remagnetized paleozoic cratonic carbonates a rock magnetic study hysteresis measurements lowrie fuller tests cisowski tests and low temperature demagnetization experiments on samples of the knox dolomite trenton limestone and onondaga limestone indicate that the remanence in these remagnetized carbonate units resides principally in single domain magnetite in contrast to previous interpretations volumetrically however a significant fraction of the magnetite is coarser grained as previous scanning electron microscopic work on magnetic extracts has shown these conclusions are based mainly on the characteristic wasp waisted shape of the hysteresis loops and on the anomalously high ratios of remanent coercivity to bulk coercivity both of which clearly indicate a bimodal distribution of coercivities grain sizes the magnetization is controlled mainly by cubic magnetocrystalline anisotropy consistent with the spheroidal particles commonly observed in extracts hysteresis trends show that especially the finest particles lack shape anisotropy in view of these conclusions the two components of natural remanence in these rocks are interpreted as 1 a late paleozoic kiaman chemical remanence carried by single domain diagenetic magnetite and 2 a cenozoic thermoviscous overprint residing principally in coarser pseudosingle domain and multidomain magnetite also of late paleozoic diagenetic origin

an integrated paleomagnetic rock magnetic and geochemical study of the marcellus shale in the valley and ridge province in pennsylvania and west virginia an integrated paleomagnetic rock magnetic and diagenetic study of the devonian marcellus subgroup from threefolds in the valley and ridge province in pennsylvania and west virginia indicates that the unit contains an intermediate temperature chemical remanent magnetization crm with south southeast declinations and shallow negative inclinations residing in pyrrhotite and a crm with more southerly declinations and shallow positive inclinations residing in magnetite rock magnetic results confirm the presence of pyrrhotite and magnetite tilt tests indicate that pyrrhotite and magnetite crms are syntilting to posttilting and paleopoles for both crms are similar and plot on the permian part of the apparent polar wander path for north america the marcellus subgroup has a complex paragenetic sequence which includes bitumen deposition and vein formation the magnetite and pyrrhotite crms formed in the permian probably due to burial diagenetic processes and not orogenic fluids the base of the unit contains the highest total organic content toc values and highest magnetic intensities both of which decrease up section this connection between toc and magnetic intensity suggests that the magnetite formed as a result of the maturation of the organic matter although more work is needed to test this hypothesis the pyrrhotite may have formed as a result of thermochemical sulfate reduction involving organic matter during the production of methane in this gas reservoir the similar permian crm ages may be explained by thrusting which resulted in rapid burial of the marcellus subgroup as it passed through the oil window and into the gas window quickly producing magnetite and pyrrhotite respectively

remagnetization by basinal fluids testing the hypothesis in the viola limestone southern oklahoma migration of orogenic or basinal fluids is a recently invoked mechanism to explain the widespread presence of late paleozoic secondary magnetizations in the rocks of north america paleomagnetic and geochemical results from the ordovician viola limestone in southern oklahoma are evaluated to assess the role of basinal fluids in leading to secondary magnetizations in the unit the viola limestone contains what we interpret to be a pervasive pennsylvanian synfolding magnetization residing in magnetite and a localized permian magnetization which resides in hematite and occurs in alteration zones around mineralized veins both secondary magnetizations are interpreted as chemical remanent magnetizations crm based on low burial temperatures and the presence of authigenic magnetic phases the relative proportion of the permian crm in hematite gradually decreases whereas the magnetite crm increases with distance from the veins fluid inclusion and sr isotope studies indicate that the vein mineralization calcite with mississippi valley type oxides and sulfides precipitated from basinal fluids which were warm saline and radiogenic the radiogenic 87sr 86sr values of the limestones in the alteration zones and the fact that there is more significant alteration closer to the veins suggests that the basinal fluids were also responsible for alteration in the limestones the coincidence of the geochemical and remagnetization trends suggests that the permian crm dates the migration of basinal fluids through the veins geochemical results from the viola limestone containing the pervasive crm indicate that it is relatively unaltered with no evidence for basinal fluids the lack of evidence for basinal fluids suggests that other mechanisms for the origin of the pervasive crm need to be tested the results of this study indicate that flow of basinal fluids was focused in veins and only locally altered the host limestone

geochemical constraints on the origin of secondary magnetizations in the cambro ordovician royer dolomite arbuckle mountains southern oklahoma abstract geochemical and paleomagnetic results from cambro ordovician royer dolomite in the arbuckle mountains southern oklahoma suggest a connection between dolomite type and magnetizations one dolomite type which is most common in the vicinity of the arbuckle anticline has a dull luminescence low 18 o values coeval to slightly lower 87 sr 86 sr ratios and contains an easterly cambro ordovician magnetization in magnetite to the southeast closer to the ouachita mountain front most of the royer dolomite contains a southeasterly and shallow magnetization in magnetite that is interpreted to be late paleozoic in age in contrast to the other dolomites these dolomites contain abundant authigenic k feldspar and pyrite radiogenic 87 sr 86 sr ratios and have a bright red luminescence all of which are consistent with alteration by basinal fluids at one site a stromatolitic bioherm dolomites similar to those at the arbuckle anticline are surrounded by the altered dolomites the distribution of specimen directions at this site is streaked between a cambro ordovician and late paleozoic direction the results of this study suggest a connection either direct by causing precipitation or indirect by increasing permeabilities for another fluid between a radiogenic fluid and a chemical magnetization in magnetite the relatively unaltered dolomites at the stromatolitic bioherm site escaped the almost pervasive alteration and remagnetization caused by the basinal fluids close to the ouachita mountains a potential source for the fluids

age of the sherman type zn pb ag deposits mosquito range colorado the sherman type zn pb ag dolomite deposits in central colorado are hosted in dolostones of the early mississippian leadville formation paleomagnetic analysis using progressive alternating field and thermal demagnetization and isothermal remanent magnetization acquisition methods was performed on specimens from samples at 37 sites in the sherman type continental chief peerless ruby sacramento and sherman deposits in their host rocks in the 72 ma pando porphyry sill s and in the 40 ma leadville type black cloud massive sulfide deposit paleomagnetic fold contact and breccia tests were performed to test for the antiquity of the magnetizations the results are interpreted to indicate that the leadville carbonates were regionally dolomitized at 308 6 1 ma in the early pennsylvanian and that the sherman type deposits were emplaced at 272 18 1 ma during the early permian after northeast trending block faulting karstification and 4 1 km of sedimentary burial possibly as the result of subsurface gravity driven fluid flow related to the ouachita marathon orogen following late ouachita marathon or earliest laramide late cretaceous folding the remanence in the sherman type deposits and the leadville dolostone rocks within the contact alteration zone of the 72 ma pando porphyry sill s was reset to acquire a late cretaceous normal characteristic remanent magnetization thereafter the black cloud leadville type massive sulfide deposit was magnetized in the eocene to acquire a reversed polarity characteristic remanent magnetization that was not found in the sherman type deposits

crustal studies of the koyna region using explosion data from deep seismic soundings abstract this study is based on the seismic data collected as a result of explosions carried out during the 1976 and 1978 deep seismic sounding dss field operations in the koyna region these shots were exploded from twelve shot points by the national geophysical research institute along the guhagar chorochi and kelsi loni profiles refraction studies of the records reveal a two layered crust the top layer consists 17 km of granite and the second layer 19 km of basalt giving the average depth of the moho as 36 km in the region the velocities of the phases pg p and pn have been computed as 5 82 0 01 6 61 0 05 and 8 23 0 05 km sec respectively and those of sg s and sn as 3 41 0 00 4 09 0 07 and 4 60 0 08 km sec respectively the shear wave velocity in the basement rock has been found to be lower in comparison with other regions of the peninsular india in some cases reflections were recorded both from the moho as well as from the intermediate layer these reveal a crustal thickness of 39 km with 19 km of granitic and 20 km of basaltic layers coda signal durations from dss explosions recorded by microearthquake seismographs indicate a lateral heterogeneity in the crust on either side of karad in an east west direction

scanning and transmission electron microscope observations of magnetite and other iron phases in ordovician carbonates from east tennessee previous paleomagnetic observations for the carbonates of the lower ordovician knox group have indicated that ancient magnetizations in these rocks are of the same age as the late paleozoic alleghenian orogeny rock magnetic properties strongly suggest magnetite as the carrier of the magnetization but the textural and crystalline characteristics sizes morphologies and mineral associations of these magnetites are poorly known we have examined magnetic extracts and iron oxides in thin sections with scanning sem and scanning transmission stem electron microscope techniques to determine whether the observed iron oxide grain textures match the rock magnetic properties and paleomagnetic inferences about the mode of formation of the magnetic carriers several different forms of magnetite in limestones and dolomites which in places are host to mississippi valley type deposits are documented by imaging and energy dispersive analysis using sem and stem by x ray diffraction and electron diffraction patterns using stem the magnetite is either spherical with a dimpled surface or nonspherical in the form of void filling single grains or grain aggregates most of the iron oxides have the composition of pure end member magnetite but occasional titanomagnetite and hematite including rare zincian hematite have been observed only in limestone wherever found in thin section nonspherical magnetites occur in association with secondary dolomite potassium feldspar illite and quartz some iron oxides have in fact inclusions of k feldspar and quartz some of the magnetite spherical and nonspherical is polycrystalline this implies that the larger observed grains may consist of single domains or pseudo single domains this provides an explanation of the observed rock magnetic properties that apparently reflect the presence of single domain but interacting subgrains on the basis of remanent coercivities and blocking temperatures we interpret the pure end member magnetite to be authigenic having formed at approximately the same time as the k feldspars which in nearby areas have yielded late paleozoic radioisotopic ages 278 322 ma the knox carbonates therefore are inferred to carry a chemical remanent magnetization iron rich clays or original iron titanium oxides in the carbonates may have been the source materials for at least some of the secondary magnetite as it formed through complete dissolution precipitation processes these processes require rock fluid interactions which are thought to be related to migrating connate brines during the alleghenian orogeny

crustal and uppermost mantle structures in the frontal himalaya and indo gangetic basin using surface wave tectonic implications abstract characteristics of dispersion curves of rayleigh and love waves of 2005 kashmir earthquake and its aftershocks are utilized to investigate the sub surface structural variations within the northern margin of the indian continent i e indo gangetic plains and the frontal part of the northwestern himalaya surface waves of these earthquakes recorded in the broad band seismometers bbs installed at ajmer delhi and shimla were used for this investigation estimated group velocities along three paths from earthquake source region to these stations are in the range of 2 17 km s to 3 94 km s which are sufficient to investigate the crustal and uppermost mantle structures paths covering northern margin of the indian continent has very low group velocities for periods less than 10 s that indicate presence of thick sediments high differences are observed between love and rayleigh wave group velocities for the paths crossing himalayan wedge that can be ascribed to the effect of anisotropy due to india eurasia collision the inversion of dispersion curves was performed to investigate sub surface shear wave velocity structure and variation of anisotropy with depth for crust and uppermost mantle a 6km thick sediments divided into two layers unconsolidated and consolidated are seen in the indo gangetic plain deposited above underthrusting indian plate the conrad and moho depths increase from ajmer the southernmost station in the igp to shimla the station lying in the himalayan wedge this shows the dipping geometry of the indian plate the average moho depth along these paths from earthquake source to ajmer station is 42 5 km to delhi station is 44 km and to shimla station is at 46 km average values of conrad depth for these ray paths are 18 5 km 19 5 km and 26 5 km respectively the s wave velocity along ajmer path is higher than that along the other two paths this may be due to lateral heterogeneity of the crust and mantle for the study area frontal western himalaya is anisotropic in nature whereas the igp region is not anisotropy effect in the western himalaya is most pronounced in the lower crustal material of the underthrusted indian plate it is quite large in the uppermost mantle below the frontal himalayan region we infer that anisotropy in the lower crust and uppermost mantle could be due to development of preferably oriented folds faults and fractures and possible reorientation of crystals as a consequence of ongoing deformation caused by continent continent collision

coastline responses to changing storm patterns 1 researchers and coastal managers are pondering how accelerated sea level rise and possibly intensified storms will affect shorelines these issues are most often investigated in a cross shore profile framework fostering the implicit assumption that coastline responses will be approximately uniform in the alongshore direction however experiments with a recently developed numerical model of coastline change on a large spatial domain suggest that the shoreline responses to climate change could be highly variable as storm and wave climates change large scale coastline shapes are likely to shift causing areas of greatly accelerated coastal erosion to alternate with areas of considerable shoreline accretion on complex shaped coastlines including cuspate cape and spit coastlines the alongshore variation in shoreline retreat rates could be an order of magnitude higher than the baseline retreat rate expected from sea level rise alone

remagnetization of lower cretaceous limestones from the southern pyrenees and relation to the iberian plate geodynamic evolution paleomagnetic study 34 sites of thick cretaceous 5000 m marine carbonate strata from the organya basin ob in the southern pyrenees reveals a uniformly normal polarity characteristic remanence with varying declination d berriasian barremian d 295 o aptian albian d 348 o upper cretaceous d 354 o that resides in magnetite and predates late cretaceous tertiary folding the lack of reverse polarity magnetizations in the berriasian barremian series together with their distinct hysteresis properties that are typical of remagnetized carbonates elsewhere are taken as evidence for a secondary overprint in the lower part of the succession a hypothesized age of remagnetization near the barremian aptian boundary fits with a major tectosedimentary event in the basin that changed deposition from platform to basinal conditions and increased subsidence during the aptian the angular difference 53 o between declination from the remagnetized strata and the mean for aptian albian strata indicates that a counterclockwise rotation occurred between the two acquisition times part of this rotation is interpreted to be local and due to slip variation along strike of a normal fault that bounded the basin and tilted the pre aptian series this cretaceous extensive phase is framed in the rift evolution of the northern margin of the iberian plate the inferred remagnetization age within the ob falls within the range of previously inferred widespread cretaceous remagnetization events affecting the iberian plate in the ob remagnetization is speculated to have taken place through chemical burial diagenetic origin rather than simple thermoviscous resetting

influence of nearshore sediment dynamics on the distribution of heavy mineral placer deposits in sri lanka beach sediments in sri lanka contain industrial grade heavy mineral occurrences samples of both offshore and onshore sediments were collected to examine the provenance mineralogy and geochemical compositions of the heavy mineral occurrences coastal morphodynamic changes along the coastline of sri lanka were analyzed using the time series satellite images these coastal morphodynamic changes were used to identify the prominent directions of monsoon influenced longshore currents coastal sediment accretion and depositional trends and their relationships to the provenance of the heavy minerals results show the concentrations of detrital ilmenite zircon garnet monazite and rutile vary in the onshore and offshore sediments the heavy mineral potential of the northeastern coast is high average contents of about 45 50 in the verugal deposit 70 85 in the pulmoddai deposit and 3 5 5 0 in offshore samples stretching from nilaveli to kokkilai compared to sediments in southwest average content about 10 in onshore sediments and 2 in offshore sediments from the mouth of the gin river therefore no economic grade heavy mineral placers were identified in the offshore environments the high concentrations of heavy minerals in beach sediments and low concentrations in offshore sediments suggest operation of a panning system in the surf zone to form enriched placer deposits major and trace element compositions of beach sediments show marked enrichments of tio2 fe2o3 la ce zr cr nb th and v compared to average upper continental crust ucc values analysis of prominent coastal longshore transport patterns identifies bidirectional sediment transport in the northeast coast of sri lanka in the southwestern coast two transport directions occur with anti clockwise transport from galle to hambantota and clockwise transport from hikkaduwa to wadduwa the heavy minerals in the placers were mainly derived from precambrian metamorphic rocks and transported to the coast through the river systems of sri lanka

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

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

palaeomagnetic cleaning strategies abstract cleaning is a term used in palaeomagnetism to refer to laboratory methods designed to demagnetize preferentially the less stable components of magnetization although the diversity of methods suggests that there is a wide choice available this is illusory except in simple cases the wrong cleaning strategy may yield misleading results cleaning methods include thermal magnetic alternating field or a f low temperature chemical shock and microwave cleaning a cleaning strategy involves one or more cleaning methods applied in a specific sequence the design of a strategy is made easier with the a priori knowledge of magnetic mineralogy and granulometry or in other words rock magnetic properties although not a substitute for other rock magnetic experiments the variation of low field susceptibility with temperature k t not only provides information on magnetic mineralogy and granulometry but it also draws attention to chemical alteration that may occur during thermal cleaning apart from the rapid though reversible decrease of k associated with curie temperatures other diagnostic k t features include the low temperature about 140 c peak typical of multidomain md magnetite the high temperature hopkinson peak typical of fine grained magnetite and other magnetic minerals and the classic lepidocrocite maghemite haematite profile which is irreversible examples are given where the remanence caused by lightning can be effectively eliminated only by applying a f or low temperature lt pre treatment such remanence may be an isothermal remanent magnetization irm or a combination of irm and anhysteretic remanent magnetization arm as the unblocking temperature of relatively low coercivity md grains may extend to high temperature it is often desirable to suppress md remanence an example is given of palaeointensity determination with the without lt pre treatment the nature of the lt transition is briefly addressed in the light of a rare double low temperature peak which may reflect both the isotropic point and the verwey transition

complexities in barrier island response to sea level rise insights from numerical model experiments north carolina outer banks using a morphological behavior model to conduct sensitivity experiments weinvestigate the sea level rise response of a complex coastal environment to changes ina variety of factors experiments reveal that substrate composition followed in rankorder by substrate slope sea level rise rate and sediment supply rate are the mostimportant factors in determining barrier island response to sea level rise we find thatgeomorphic threshold crossing defined as a change in state e g from landward migratingto drowning that is irreversible over decadal to millennial time scales is most likely tooccur in muddy coastal systems where the combination of substrate composition depth dependent limitations on shoreface response rates and substrate erodibility mayprevent sand from being liberated rapidly enough or in sufficient quantity to maintain asubaerial barrier analyses indicate that factors affecting sediment availability such aslow substrate sand proportions and high sediment loss rates cause a barrier to migratelandward along a trajectory having a lower slope than average barrier island slope therebydefining an effective barrier island slope other factors being equal such barrierswill tend to be smaller and associated with a more deeply incised shoreface therebyrequiring less migration per sea level rise increment to liberate sufficient sand to maintainsubaerial exposure than larger less incised barriers as a result the evolution of larger lessincised barriers is more likely to be limited by shoreface erosion rates or substrateerodibility making them more prone to disintegration related to increasing sea level riserates than smaller more incised barriers thus the small deeply incised north carolinabarriers are likely to persist in the near term although their long term fate is less certainbecause of the low substrate slopes that will soon be encountered in aggregate results point to the importance of system history e g previous slopes sediment budgets etc in determining migration trajectories and therefore how a barrier island will respondto sea level rise although simple analytical calculations may predict barrier responsein simplified coastal environments e g constant slope constant sea level rise rate etc our model experiments demonstrate that morphological behavior modeling is necessary toprovide critical insights regarding changes that may occur in environments havingcomplex geometries especially when multiple parameters change simultaneously

recent acceleration in coastal cliff retreat rates on the south coast of great britain rising sea levels and increased storminess are expected to accelerate the erosion of soft cliff coastlines threatening coastal infrastructure and livelihoods to develop predictive models of future coastal change we need fundamentally to know how rapidly coasts have been eroding in the past and to understand the driving mechanisms of coastal change direct observations of cliff retreat rarely extend beyond 150 y during which humans have significantly modified the coastal system cliff retreat rates are unknown in prior centuries and millennia in this study we derived retreat rates of chalk cliffs on the south coast of great britain over millennial time scales by coupling high precision cosmogenic radionuclide geochronology and rigorous numerical modeling measured 10be concentrations on rocky coastal platforms were compared with simulations of coastal evolution using a monte carlo approach to determine the most likely history of cliff retreat the 10be concentrations are consistent with retreat rates of chalk cliffs that were relatively slow 2 6 cm y 1 until a few hundred years ago historical observations reveal that retreat rates have subsequently accelerated by an order of magnitude 22 32 cm y 1 we suggest that acceleration is the result of thinning of cliff front beaches exacerbated by regional storminess and anthropogenic modification of the coast

late paleozoic magnetization of mineralized and unmineralized ordovician carbonates from east tennessee evidence for a post ore chemical event thermal demagnetization studies on samples from mineralized and unmineralized rocks in the lower ordovician knox group of east tennessee reveal a mean direction of d i 157 18 95 7 7 k 52 9 after 60 unfolding combining stable endpoint and remagnetization circle data although not significant at the 95 confidence level the fold test is suggestive of a synfolding alleghenian age of the magnetization the magnetization cannot be postfolding i e permian or younger because the in situ directions do not resemble those for post carboniferous times the magnetization is unlikely to be much older than the folding because the directions with respect to bedding yield a paleopole characteristic of the early permian but unlike poles for pre late carboniferous times characteristic magnetizations from mineralized and unmineralized collapse breccias are in good agreement and fail the conglomerate test the best estimate for the paleopole resulting from this study falls at 40 n 126 e within the late carboniferous segment of the north american paleozoic apparent polar wander path thus the magnetization is interpreted as synfolding and secondary due to widespread kiaman remagnetization blocking temperatures of up to 520 c and the acquisition of isothermal remanent magnetization suggest magnetite as the carrier of the magnetization scanning electron microscopy and energy dispersive analysis of magnetic extracts from limestone samples reveal abundant magnetite spheres secondary dolomites have the same magnetic characteristics as the primary limestones and it is inferred that similar magnetite spheres are the carriers of their magnetization because this magnetization and therefore its carrier occurs in sphalerite and secondary dolomite it must be coeval with or younger than the ore which itself is thought to be of middle to late paleozoic age it is argued that the magnetization was acquired during growth of magnetite associated with a late paleozoic chemical event

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

an evolving research agenda for human coastal systems within the broad discourses of environmental change sustainability science and anthropogenic earth surface systems a focused body of work involves the coupled economic and physical dynamics of developed shorelines rapid rates of change in coastal environments from wetlands and deltas to inlets and dune systems help researchers recognize observe and investigate coupling in natural non human morphodynamics and biomorphodynamics this same intrinsic quality of fast paced change also makes developed coastal zones exemplars of observable coupling between physical processes and human activities in many coastal communities beach erosion is a natural hazard with economic costs that coastal management counters through a variety of mitigation strategies including beach replenishment groynes revetments and seawalls as cycles of erosion and mitigation iterate coastline change and economically driven interventions become mutually linked emergent dynamics of two way economic physical coupling is a recent research discovery having established a strong theoretical basis research into coupled human coastal systems has passed its early proof of concept phase this paper frames three major challenges that need resolving in order to advance theoretical and empirical treatments of human coastal systems 1 codifying salient individual and social behaviors of decision making in ways that capture societal actions across a range of scales thus engaging economics social science and policy disciplines 2 quantifying anthropogenic effects on alongshore and cross shore sediment pathways and long term landscape evolution in coastal zones through time including direct measurement of cumulative changes to sediment cells resulting from coastal development and management practices e g construction of buildings and artificial dunes bulldozer removal of overwash after major storms and 3 reciprocal knowledge and data exchange between researchers in coastal morphodynamics and practitioners of coastal management future research into human coastal systems can benefit from decades of interdisciplinary work on the complex dynamics of common pool resources from computational efficiency and new techniques in numerical modeling and from the growing catalog of high resolution geospatial data for natural and developed coastlines around the world

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

rock magnetism of remagnetized paleozoic carbonates low temperature behavior and susceptibility characteristics we have conducted a new set of rock magnetic experiments on samples of remagnetized paleozoic carbonates of eastern north america these experiments were designed to investigate the origin of the unusual hysteresis behavior of these rocks by evaluating 1 the importance of ferrimagnetic pyrrhotite as a remanence carrier and 2 the sources of low field susceptibility low temperature measurements of saturation isothermal remanent magnetization sirm indicate that the pyrrhotite magnetic transition at 32 k is absent in the trenton and onondaga limestones of new york this transition is observed but poorly expressed in the knox group of east tennessee room temperature sirms cooled to 10 k in zero field lose a small fraction of their intensity between 30 and 35 k samples from all three formations show a broad peak in irm intensity at about 200 k which is typical of pyrrhotite in the trenton and onondaga samples the ferrimagnetic component of low field susceptibility is significantly larger than the ratio mrs hcr and is thus probably due dominantly to magnetite in some of the knox samples the reverse is true suggesting an important pyrrhotite contribution for all of the samples the ferrimagnetic susceptibility normalized by the saturation magnetization is anomalously high about a factor of 5 or 10 higher than the typical value for magnetite we believe that this indicates a very substantial contribution from superparamagnetic particles strong frequency dependence of susceptibility and very high ratios of anhysteretic to saturation remanence confirm the importance of ultrafine particles spanning the superparamagnetic single domain boundary all three of these chemically remagnetized carbonates units exhibit the following properties which have not previously been found together for any rock or synthetic analog and which therefore appear to constitute a diagnostic set of rockmagnetic criteria for recognizing chemically remagnetized rocks mrs ms 0 89 hcr hc 0 6 k ms 50 m a arm sirm 20 ka mrs hcr 50

modeling large scale shoreline sand waves under oblique wave incidence waves develop with wavelengths between 2 and 5 km they migrate downdrift at about 0 5 km yr and they reach amplitudes up to 120 m within 13 years larger wave obliquity higher waves and shorter wave periods strengthen the shoreline instability cross shore transport is essential for the instability and faster cross shore dynamics leads to a faster growth of the sand waves simulations with variable wave incidence angles alternating between 60 and 30 show that a large proportion of high angle waves is required for spontaneous sand wave formation at least 80 insight is provided into the physical mechanism behind high angle wave instability and the occurrence of a optimal length scale for sand wave growth the generic model results are consistent with existing observations of shoreline sand waves in particular with those along the southwest coast of africa

surface wave and lithospheric structure across the northwestern part of the indian peninsula group velocities of fundamental mode rayleigh and love waves have been obtained across the central highlands in the northwestern part of the indian peninsula and across the plateau region of the peninsula such data across the latter region were also obtained earlier and revealed model lithosphere ip11 for this region data of the two regions are similar and show that the lithospheric model ip11 continues from the plateau region to the central highlands the model ip11 has been verified by comparing observed love wave forms with synthetics ones

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

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

remagnetization of the tonoloway formation and the helderberg group in the central appalachians testing the origin of syntilting magnetizations summary palaeomagnetic rock magnetic geochemical and strain studies of the helderberg group and the tonoloway formation in the valley and ridge province of west virginia were performed to test the origin of syntilting magnetizations and to test the mechanisms of chemical remanent magnetization crm acquisition the test for a connection between strain and remagnetization was performed by comparing the types and levels of strain with the magnetic properties between the generally coarse grained thickly bedded helderberg and the thinly bedded and finer grained tonoloway standard tilt tests as well as optimal differential untilting from two transects on the wills mountain anticline indicate that the helderberg contains a pervasive late syntilting 30 per cent untilting characteristic remanent magnetization chrm whereas the tonoloway contains a well defined early syntilting chrm 1 76 per cent untilting as well as a chrm 2 which is similar to the chrm in the helderberg the chrms reside in magnetite the rock magnetic results from the two units are similar although the helderberg samples have a finer apparent grain size perhaps as a result of magnetic hardening strain data reveal an apparent correlation between the syntilting magnetizations and types degrees of pressure solution strain pressure solution strain is higher in the helderberg and lower in the tonoloway strain may have caused rotation of magnetic minerals but it not clear that the differences in strain between the units were high enough to cause the rotations that are needed to explain the tilt test results several other viable hypotheses were also investigated one hypothesis is a strain enhanced chemical process that caused dissolution and precipitation of new magnetite in solution structures during folding a preliminary test of this hypothesis produced inconclusive results another hypothesis consistent with some of the characteristics of the magnetizations in the helderberg and tonoloway units is that the rocks were partially to completely remagnetized by a piezoremanent remagnetization process geochemical results show that origin of the remanence carrying grains cannot be attributed to orogenic type fluids but were probably caused by a burial diagenetic process

modes and emergent time scales of embayed beach dynamics in this study we use a simple numerical model the coastline evolution model to explore alongshore transport driven shoreline dynamics within generalized embayed beaches neglecting cross shore effects using principal component analysis pca we identify two primary orthogonal modes of shoreline behavior that describe shoreline variation about its unchanging mean position the rotation mode which has been previously identified and describes changes in the mean shoreline orientation and a newly identified breathing mode which represents changes in shoreline curvature wavelet analysis of the pca mode time series reveals characteristic time scales of these modes typically years to decades that emerge within even a statistically constant white noise wave climate without changes in external forcing suggesting that these time scales can arise from internal system dynamics the time scales of both modes increase linearly with shoreface depth suggesting that the embayed beach sediment transport dynamics exhibit a diffusive scaling

seismic heterogeneities in the indian lithosphere abstract rayleigh wave group velocity distributions over the indian region were obtained by the backus gilbert method for time periods 15 25 40 50 and 60 s the observed velocity variations reveal sharp lithospheric heterogeneities in this region southern peninsular india is marked by high velocities in contrast to the northern indo gangetic plain and the himalaya highest surface wave velocities are observed over the southern part of the deccan traps and the dharwar craton whereas the metamorphic terrains and rift zones exhibit anomalous low velocities the nepal himalaya and indo burmese collision zones are characterised by contrasting velocities which reflect their diverse orogenesis the bay of bengal is marked by an anomalous 6 12 higher velocity as compared with the indian continental region for the periods 25 50 s

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

low temperature behavior of single domain through multidomain magnetite abstract we have investigated the low temperature behavior of a suite of grown synthetic and natural magnetites that span single domain sd and multidomain md behavior synthetic samples had been grown in the laboratory either in an aqueous medium or in glass natural samples included sd magnetites occurring in plagioclase and truly md magnetites in the form of large octahedra in all experiments a sample was first given a saturation remanence at room temperature next moment was measured continuously during cooling and warming between 230 k and 60 k similar to results reported earlier by other workers magnetic memory is large in sd samples whereas truly md samples are almost completely demagnetized by cycling between room temperature and 60 k pseudo single domain samples exhibit behavior that is intermediate with respect to that of the sd and truly md states when data from this study are combined with data obtained by hartstra 10 from sized natural magnetites it is found that the percentage of total remanence that survives cycling between room temperature and 60 k decreases linearly with the logarithm of grain size and thus with increasing number of domains this relation suggests that memory can provide a reasonable estimate of grain size in those magnetite bearing rocks for which these samples provide good analogues remarkably some of the large natural octahedra provide a magnified view of md response to low temperatures and thus reveal two surprising and intriguing types of behavior first below approximately 180 k these octahedra demagnetize through a series of large barkhausen jumps second near 117 k these same octahedra exhibit a wild zone where magnetic moment executes large random excursions we interpret these two phenomena as direct evidence for the unpinning and irreversible displacement of domain walls in response to the drop in coercivity and possibly the broadening of domain walls as temperatures drop toward the isotropic point one implication of this behavior is that cooling to progressively lower temperatures could provide an effective method for stepwise removal of paleomagnetic components carried by md grains even without passage through the isotropic point of magnetite

remagnetization of the folded belden formation northwest colorado paleomagnetic and geochemical results are used to evaluate the origin of an apparent synfolding magnetization in belden formation pennsylvanian limestones on an asymmetric fold in colorado the natural remanent magnetizations contain three components a modern viscous magnetization removed at low temperatures a reversed tertiary magnetization declination d 186 7 inclination i 54 6 of thermoviscous origin removed at intermediate temperatures and an apparently synfolding late cretaceous early tertiary characteristic magnetization d 338 7 e i 62 5 precision parameter k 54 9 radius of 95 probability cone 95 5 9 65 unfolding removed by 580 c hysteresis properties suggest that the characteristic magnetization resides in single domain magnetite low burial temperatures and the presence of authigenic magnetite are consistent with a chemical origin for this magnetization the 87sr 86sr values 0 7088 0 7100 show the limestones to be radiogenic with 87sr enriched halos around calcite cemented tectonic fractures there is no control on the distribution and intensity of the magnetization by the veins or structural position e g highly mineralized versus less mineralized rock lithology rather than fluid alteration controls the magnetization fecal pellets contain pyrite with alteration rims identified as magnetite by scanning transmission electron microscope x ray diffraction patterns selective demagnetization has established that the fecal pellets carry the characteristic magnetization it is not possible to unequivocally establish whether the characteristic magnetization is synfolding or prefolding a synfolding magnetization caused by the syndeformational mineralizing fluids however can be ruled out structural modification of a prefolding component and a synfolding piezoremanent magnetization cannot be ruled out but are not considered likely mechanisms of remanence acquisition overprinting of a prefolding chemical magnetization by a postfolding viscous magnetization residing in multidomain grains is a likely explanation for the synfolding test result the replacement of pyrite by magnetite is interpreted as prefolding in origin perhaps triggered by an oxidizing fluid or by diagenesis of hydrocarbons

contradictory magnetic polarities in sediments and variable timing of neoformation of authigenic greigite abstract in several recent published studies paleomagnetic results from greigite bearing sediments reveal characteristic remanences that are anti parallel to those carried by coexisting detrital magnetic minerals and polarities that are opposite to those expected for the age of the rock unit these observations have important implications for the reliability of paleomagnetic data from greigite bearing sediments we have investigated the origin of such contradictory magnetic polarities by studying the formation mechanisms of greigite in mudstones from the lower gutingkeng formation southwestern taiwan scanning electron microscope observations indicate that the gutingkeng greigite has three modes of occurrence including nodular framboidal and matrix greigite microtextural observations including transection of bedding by iron sulfide nodules with no deviation of sediment textures the presence of partially dissolved edges around detrital and early diagenetic phases and neoformation of greigite and fe rich clays around detrital phyllosilicates indicate that all three types of greigite have a diagenetic origin that post dates early diagenetic pyrite in addition paleomagnetic data yield contradictory polarities even for greigite bearing sister samples from the same stratigraphic horizon the data are collectively interpreted to indicate that neoformation of the gutingkeng greigite occurred after partial dissolution of syngenetic or early diagenetic pyrite the timing of greigite formation can apparently vary enough to give contradictory polarities for different greigite components even within a single stratigraphic horizon direct petrographic observation of authigenic magnetic iron sulfide phases as carried out in this study can provide important constraints on formation mechanisms and timing of remanence acquisition for these minerals and suggests that care should be taken when interpreting magnetostratigraphic data from greigite bearing sediments

multidisciplinary approach to an extensional syncline model for the mesozoic cameros basin n spain abstract in this paper we explore the possibility of reconstructing the initial geometry of inverted basins using combined geophysical and geological methods seismic reflection profiles paleomagnetism analogue modelling and 3d geometrical analysis these techniques allow for some unknowns in the geometry and evolution of extensional sedimentary basins mainly the normal drag reverse drag geometrical problem to be solved the example chosen for checking these techniques is the cameros basin northern iberian chain formed during the late jurassic early cretaceous and inverted during the tertiary compressional stage according to the reconstruction proposed the cameros basin can be characterised as a lens shaped syncline basin with maximum thickness of deposits of about 8000 m in its depocenter gradually diminishing toward the north and south the extensional geometry of the cameros basin is defined by 1 a large scale growth syncline over the major basement fault with southward dipping beds in the northern basin margin forming a southward opening sedimentary wedge with upward decreasing dip values large scale normal drag geometry 2 roll over anticlines at the contact between the pre rift series against the normal fault limiting the basin smaller scale reverse drag geometry the combined syncline anticline syn extensional structures were characterised by means of paleomagnetic analysis of a remagnetization acquired at the time of extension analogue models indicate that the development of syncline basin geometries in extensional settings as the one interpreted for the cameros basin is closely related to the presence of a detachment level in the pre rift sequence above the main basement faults

orogenic remagnetizations in the front ranges and inner foothills of the southern canadian cordillera chemical harbinger and thermal handmaiden of cordilleran deformation abstract paleomagnetic studies of carbonate rocks in mountain belts have been helpful to the understanding of orogenic mational origin with only one exception the a component has normal polarity in the front ranges and reverse processes the timing of deformation and the nature of fluid flow in actively deforming foreland basins most studies on shallow water carbonates indicate that their remanence is not primary but rather they record remagnetization events contemporaneous with orogeny by considering the remanent directions fold test results and rock magnetic properties and tying these results to complementary structural geochronological and geochemical studies we are able to interpret deformation history hydrological environment and orogenic diagenesis we study the relationship between remagnetization and deformation of paleozoic carbonates of the front ranges and inner foothills of the southern canadian rockies the magnetic properties are remarkably constant along 500 km strike length as sampled at 124 sites through 4 transects primary paleozoic remanent directions which would have shallow inclination are never observed rather the paleomagnetic signal is dominated by geographically persistent remagnetizations characterized by steep inclination as well as a soft present field overprint we observed two distinctive secondary magnetizations named the a and b components carried by fine grained magnetite pervasive diagenesis induced the a component a total chemical remanent remagnetization poles for the a component are better concentrated after bedding correction indicating a pre or early syndefor polarity in the inner foothills pole positions polarity and geological and thermal constraints indicate that the a component was acquired diachronously in advance of the eastward migrating cordilleran tectonic wedge subsequently an intermediate temperature partial thermo remanent remagnetization the b component was superimposed on large regions of the front ranges and inner foothills b component directions are brought into optimal concentration by differential untilting of 0 to 50 indicating that the component was acquired after the rocks were incorporated into the orogenic wedge but before the end of contractional deformation the b component is strongest within a couple of kilometers of the frontal thrust of the front ranges the relative magnitude of the b to a components and the maximum unblocking temperature of the b component decrease away from the frontal thrust over about 30 km both to the west and to the east the b component thermal overprint was attained by 250 c heating in response to tectonic or possibly sedimentary loading it was preserved by a rapid cooling accompanying a differential uplift and erosion of up to 8 km in the vicinity of the frontal thrust late in or post dating its local tilting history the likely cause was uplift of the exposed structural panel by contraction of younger underlying thrust structures

tg plus a pyrolysis method for following maturation of oil and gas generation zones using tmax of methane abstract thermogravimetric fourier transform infrared spectroscopy tg ftir analyses were carried out on two sets of isolated kerogens covering a wide maturity range from low mature 0 46 r o through the end of oil and gas generation maximum r o 5 32 data onweight percent and t max for evolution of methane volatile tars ethylene so 2 nh 3 co 2 and co are reported the t max of methane shows the most consistent response to increasing maturation in both sets of samples results are comparable to those of whole rocks from an alaskan north slope well analyzed previously the collective data for both whole rocks and isolated kerogens shows a generally linear correlation between r o and t max of methane with the exception of r o of about 2 0 where a dip in the curve occurs the slope of the correlation line was steeper for the predominantly terrigenous wilcox kerogen than for more marine colorado kerogen or for the alaskan north slope whole rock samples probably reflecting differences in the chemical nature of various kerogen sets which is also reflected by differences in the shapes of the pyrolysis curves of so 2 co 2 co h 2 o and ethylene these preliminary data indicate that t max of methane is a good maturation indicator for whole rocks and isolated kerogens up to an r o of about 4 which includes all of the wet gas and a considerable portion of the dry gas generation zones this correlation was also observed for samples containing migrated bitumen where it was not possible to obtain a reliable t max for the volatile tar s2 peak the more terrigenous wilcox kerogens also showed a good correlation of the t max of ethylene with r o t max of ammonia evolution did not correlate with maturity and occurred 100 200 c lower than previously found for whole rocks consistent with a whole rock source of pyrolytic ammonia for alaskan whole rock samples hi and oi indices were calculated in several ways and plotted to reflect kerogen type as well as both the residual oil and gas generation potential the ratio of pyrolyzable to combustible sulfur evolved as so 2 was independent of maturity and showed a clear difference between the more terrigenous wilcox kerogens and the more marine colorado kerogens

recent shifts in coastline change and shoreline stabilization linked to storm climate change since cuspate coastlines are especially sensitive to changes in wave climate they serve as potential indicators of initial responses to changing wave conditions previous work demonstrates that cape hatteras and cape lookout north carolina which are largely unaffected by shoreline stabilization efforts have become increasingly asymmetric over the past 30 years consistent with model predictions for coastline response to increases in atlantic ocean summer wave heights and resulting changes in the distribution of wave approach angles historic and recent shoreline change observations for cape fear north carolina and model simulations of coastline response to an increasingly asymmetric wave climate in the presence of beach nourishment produce comparable differences in shoreline change rates in response to changes in wave climate results suggest that the effect of beach nourishment is to compensate for and therefore to mask natural responses to wave climate change that might otherwise be discernible in patterns of shoreline change alone therefore this case study suggests that the effects of wave climate change on human modified coastlines may be detectable in the spatial and temporal patterns of shoreline stabilization activities similar analyses of cuspate features in areas where the change in wave climate is less pronounced i e fishing point maryland virginia and where local geology appears to exert control on coastline shape i e cape canaveral florida suggest that changes in shoreline configuration that may be arising from shifting wave climate are currently limited to sandy wave dominated coastlines where the change in wave climate has been most pronounced however if hurricane generated wave heights continue to increase large scale shifts in patterns of erosion and accretion will likely extend beyond sensitive cuspate features as the larger scale coastline shape comes into equilibrium with changing wave conditions copyright 2014 john wiley sons ltd

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

integrated rock magnetic and mineralogical study of the lower triassic sedimentary rocks from spitsbergen abstract a rock magnetic mineralogical and mossbauer spectroscopy study was undertaken on the lower triassic sediments from the west spitsbergen fold and thrust belt wsftb in svalbard as well as the foreland of this orogen for a thorough recognition of magnetic mineralogy necessary for a better constrained interpretation of paleomagnetic results sem and mossbauer spectroscopy indicate the presence of magnetite and pyrrhotite both most probably of secondary origin but altered clasts of volcanic origin and grains of ilmenite and detrital magnetite are also observed thermomagnetic curves of whole rock samples exhibit paramagnetic behavior whereas ferromagnetic separates indicate the presence of magnetite irm component analysis shows three major contributors magnetite hematite and pyrrhotite to the remanence with ferromagnetic iron oxides the most dominant identified ferromagnetic minerals display a wide range of grain size and magnetic behavior with the domination of psd particles rock magnetic characteristics of both areas are similar but sites in the fold belt were most likely remagnetized whereas those in the foreland carry the primary magnetization the age of remagnetization was estimated as pre eurekan related to rift controlled mesozoic extensional phases of the barents sea shelf clark et al 2014 and or cretaceous injections of dolerites in the svalbard archipelago nejbert et al 2011 as well as early stages of the wsftb formation however triassic remanence might persist in volcanic lithoclasts and detrital magnetite indicated along the wsftb the multicomponent nature of the nrm displaying a broad range of grain size might impede the paleomagnetic interpretation of triassic rocks in spitsbergen

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

deep electrical conductivity structure beneath the southern part of the indo gangetic plains analysis of magnetotelluric data near the southern boundary of the indo gangetic basin reveals a clear two dimensional structure two dimensional numerical modelling of the data has been carried out the e polarization response is found to be very similar to the local one dimensional response a study has been carried out to remove the screening effect on the magnetotelluric data caused by the top layer sediments after the removal of the top layer sediments a best fit model of the averaged magnetotelluric field data has been found which has a very thick resistive upper crust and a conducting lower crust the conductance of the lower crust is found to be much less than the values of lower crustal conductance obtained in eastern siberia in contrast the upper mantle below the indo gangetic plains has a resistivity significantly greater than that of the upper mantle below eastern siberia

shear velocities qβ and the frequency dependence of qβ in stable and tectonically active regions from surface wave observations summary velocities and attenuation coefficient values of rayleigh waves within the south american continent and indian subcontinent have been determined in order to study velocity structure and qp structure as well as their lateral variation in those regions single station and two station data are combined to yield dispersion and attenuation data from periods of a few seconds to periods between 60 s and 100 s for each region both types of data are inverted using differential inversion schemes this inversion process is found to sometimes allow the location of velocity discontinuities in the models directly from the dispersion data qp models obtained from the inversion process are not constrained to have high values at large depths a problem with earlier methods used to invert surface wave attenuation data the shear velocity models for the indian shield and eastern south america are similar to one another and have somewhat slower velocities than those reported for shield regions of north america the shear velocity models for the himalaya and andes are similar to one another in crustal thickness but the velocities in the andes are lower than those in the himalayas in the uppermost mantle a low velocity zone can marginally be resolved in the upper mantle beneath the himalaya but not beneath the other regions in this study qp models obtained for the stable regions of eastern north america and eastern south america exhibit similar qp values at mantle depths the indian shield however has much lower qp values in both the crust and upper mantle a result which may be related to the unusually high heat flow observed for that stable region for the tectonically active regions of western north america western south america and the himalaya is considerably lower than qp for the stable regions throughout most of the crust and upper mantle minimum mantle values appear to be about 120 for stable regions and 40 or less for tectonically active regions thus qp values in the upper mantle appear to vary regionally by a factor of 3 or more whereas shear velocities in the same regions vary by no more than 13 per cent

chemical remagnetization and burial diagenesis testing the hypothesis in the pennsylvanian belden formation colorado lower pennsylvanian belden formation carbonate rocks from colorado were subjected to paleomagnetic rock magnetic and geochemical studies to test whether there is a connection between a widespread chemical remanent magnetization crm carried by authigenic magnetite and burial diagenesis thermal demagnetization results indicate the presence of two components of natural remanent magnetization nrm after removal of a low unblocking temperature nrm 250 c remanence that is interpreted to be a modern viscous magnetization an intermediate unblocking temperature 250 400 c remanence component with normal and reversed polarity tertiary directions is interpreted to be a thermoviscous remanent magnetization many limestones also contain a high unblocking temperature 400 570 c remanence component which is interpreted to be a crm fold tests from different parts of the basin indicate that the crm was acquired either before or during laramide folding this crm is interpreted to be carried by authigenic magnetite that formed by replacement of pyrite hysteresis ratios are consistent with those reported for other remagnetized carbonates and indicate that the crm is carried by single domain pseudo single domain magnetite although elevated 87sr 86sr values indicate passage of radiogenic fluids through the limestones the results of contact vein tests do not support the hypothesis that these fluids were responsible for the crm the time of crm acquisition which varies from late paleozoic to cretaceous coincides with the modeled time of organic matter maturation in different parts of the basin this suggests that diagenetic reactions that were triggered by low to moderate burial temperatures may have caused the magnetite authigenesis and probably gave rise to the crm

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

authigenesis of magnetite in organic rich sediment next to a dike implications for thermoviscous and chemical remagnetizations rock magnetic results from organic rich sediment around a tertiary dike in scotland indicate changes in magnetic mineralogy and magnetite content as well as grain size in the contact zone sediment specimens within 85 cm of a 90 cm thick dike contain a tertiary magnetization that is equivalent in direction to the thermal remanent magnetization in the dike whereas the sediment at greater distances does not carry a stable remanence based on acquisition of isothermal remanent magnetization irm thermal decay of triaxial irms and s ratio determinations magnetite is the dominant magnetic phase in the sediment except near the dike 8 cm where hematite is abundant maximum laboratory unblocking temperatures tbmax for the magnetization are higher than predicted by a thermal cooling model at distances greater than 40 cm but the tbmax values are not corrected for gradual cooling of the dike and are therefore overestimates trends in rock magnetic parameters such as irm at 300 mt and anhysteretic remanence arm are consistent with an increasing contribution of single domain pseudosingle domain magnetite towards the dike an increase in saturation irm sirm along with a decrease in arm sirm values 25 cm from the dike also suggest an increase in multidomain magnetite low temperature experiments indicate the presence of abundant superparamagnetic magnetite changes in hysteresis parameters are consistent with changes in the relative amounts of the different magnetite size fractions towards the dike the onset of changes in the magnetite grain size budget starting at 85 cm or approximately one dike width suggests that chemical processes contributed to the remanence at temperatures as low as 220 c petrographic and geochemical studies suggest that the contact zone was not pervasively altered by hydrothermal fluids utilizing the dike as an analog for thermal processes that occur during burial the results of this study suggest that moderately elevated burial temperatures are sufficient to cause magneto chemical changes

long term non local coastline responses to local shoreline stabilization 1 the future of large scale coastline evolution will be strongly coupled to human manipulations designed to prevent erosion we explore the consequences of this coupling using a numerical model for large scale coastline evolution to compare the long term non local effects of two generalized classes of shoreline stabilization 1 beach nourishment the addition of dredged sand to an eroding beach and 2 hard structures e g seawalls groynes etc which fix the position of the shoreline without adding sand in centurial model experiments where localized stabilization is maintained in the context of changing climate forcing both forms of stabilization are found to significantly alter patterns of erosion and accretion at distances up to tens of kilometers on a cuspate cape coastline similar to the north and south carolina coast usa with stabilization applied to the eroding updrift flank of a single cape perturbations to coastline evolution are qualitatively similar within 20 km for each stabilization scenario though they differ in magnitude both updrift and downdrift of the stabilized shoreline the human signal in coastline change can extend as far as a neighboring cape approximately 100 km away but these long range effects differ for each scenario nourishment resulted in seaward growth of the stabilized cape increasing the extent that it blocked sediment flux in downdrift regions of the coast through wave shadowing when stabilized with a hard structure the cape s initial position remain fixed decreasing wave shadowing

paleomagnetism and rock magnetism of the mississippian leadville carbonate formation and implications for the age of sub regional dolomitization the mississippian leadville formation of central colorado is dolomitized near the sawatch uplift and hosts numerous pb zn ag mineral deposits paleomagnetic and rock magnetic data from several dolomite types away from centers of tertiary intrusive activity imply a late paleozoic late mississippian age for the dolomitization e g d 148 i 11 k 86 95 8 6 n 3 localities 31 samples in dolomitized units the magnetization is of diagenetic origin and was probably acquired during or soon after dolomitization tertiary thermochemical activity has overprinted dolomites close to intrusive centers data indicate that limestones removed from igneous activity were also remagnetized at the same time

instability and finite amplitude self organization of large scale coastline shapes recent research addresses the formation of patterns on sandy coastlines on alongshore scales that are large compared with the cross shore extent of active sediment transport a simple morphodynamic instability arises from the feedback between wave driven alongshore sediment flux and coastline shape coastline segments with different orientations experience different alongshore sediment fluxes so that curvatures in coastline shape drive gradients in sediment flux which can augment the shoreline curvatures in a simple numerical model this instability and subsequent finite amplitude interactions between pattern elements lead to a wide range of different rhythmic shapes and behaviours ranging from symmetric cuspate capes and bays to alongshore migrating flying spits depending on the characteristics of the input wave forcing the scale of the pattern coarsens in some cases because of the merger of migrating coastline features and in other cases because of non local screening interactions between coastline protrusions which affect the waves reaching other parts of the coastline features growing on opposite sides of an enclosed water body mutually affect the waves reaching each other in ways that lead to the segmentation of elongated water bodies initial tests of model predictions and comparison with observations suggest that modes of pattern formation in the model are relevant in nature

coupled economic coastline modeling with suckers and free riders 1 shoreline erosion is a natural trend along most sandy coastlines humans often respond to shoreline erosion with beach nourishment to maintain coastal property values locally extending the shoreline through nourishment alters alongshore sediment transport and changes shoreline dynamics in adjacent coastal regions if left unmanaged sandy coastlines can have spatially complex or simple patterns of erosion due to the relationship of large scale morphology and the local wave climate using a numerical model that simulates spatially decentralized and locally optimal nourishment decisions characteristic of much of u s east coast beach management we find that human erosion intervention does not simply reflect the alongshore erosion pattern spatial interactions generate feedbacks in economic and physical variables that lead to widespread emergence of free riders and suckers with subsequent inequality in the alongshore distribution of property value along cuspate coastlines such as those found along the u s southeast coast these long term property value differences span an order of magnitude results imply that spatially decentralized management of nourishment can lead to property values that are divorced from spatial erosion signals this management approach is unlikely to be optimal

thermoviscous remanent magnetism of columbia river basalt blocks in the cascade landslide we studied sixteen basalt samples from a landslide in the columbia river gorge to determine if they had acquired a thermoviscous remanent magnetism tvrm since the slide was emplaced about 800 years ago all samples were thermally demagnetized at 20 heating steps until 360 c where a large change in susceptibilit y was noted analysis of the directional changes during demagnetization indicates that the samples contain up to four tvrm components in addition to an nrm component the tvrm components with the lowest blocking temperatures are tightly clustered around the present field direction while the nrm directions are consistent with a random distribution as expected for a landslide deposit measurements of hysteresis parameters and thermomagnetic analyses of the samples demonstrate that the dominant magnetic mineral in the basalt is single domain magnetite the temperature at which the first tvrm component was removed ranges from 70 c to 100 c this result can be compared to nomographs that relate the time and temperature used to demagnetize a tvrm with the time and temperature at which the tvrm was acquired our results are more consistent with the nomograph of pullaiah et al 1975 than with the nomograph of middleton schmidt 1982