inclination variation in the late jurassic to eocene red beds from southeast asia lithological to locality scale approach summary shallowpalaeomagneticinclinationshavebeenfrequentlyreportedfromtheredbedsofcentral and southeast asia to trace the origin of this phenomenon inclination variation in southeast asia is examined on lithological to locality scale lithological aspect of this variation has been studied using the early cretaceous bailong and cangxi formations of the bazhong area 32 1 n 106 7 e the northern sichuan basin samples from 36 sites consisting 18 pairs of successive sandstones and mudstones layers were collected for this purpose from a synclinal structure stepwise thermal demagnetization of most samples revealed the presence of stable characteristic remanent magnetization which is generally unblocked by 680 c positive fold and reversal tests suggest a primary origin for this component yielding the early cretaceous palaeomagnetic direction of declination inclination 20 9 26 5 ks 37 2 95 4 4 n 30 10 pairs of sandstone and mudstone layers show almost identical inclinations isandstones 23 3 3 7 and imudstones 24 7 2 4 but 27 shallower than that expected from the eurasian apparent polar wander paths apwps indicating that no lithological variation in inclination has occurred location wise variation in inclination shallowing is examined through palaeomagnetic data from late jurassic to eocene red beds distributed around southeast asia based on these investigations no inclination shallowing is observed in the eastern part of the south china block scb whereas large degree of shallowing is observed in the sichuan and xining ninhe basins variation in inclination shallowing from one sedimentary basin to another could probably be caused by changes in the depositional environment the eastern part of the scb where no inclination shallowing have been observed is characterized by basin and range type tectono geological setting in contrast the foreland basins are bounded to the north by east west striking high altitude orogenic belt swift developmentofthesebasinsasaresultofflexuralsubsidenceisthemostlikelyreasonforinclination shallowing

millennial scale changes in north atlantic circulation since the last glaciation ocean circulation is closely linked to climate change on glacial interglacial and shorter timescales extensive reorganizations in the circulation of deep and intermediate depth waters in the atlantic ocean have been hypothesized for both the last glaciation1 2 3 4 5 6 and the subsequent younger dryas cold interval3 6 7 8 9 10 but there has been little palaeoceanographic study of the subtropical gyres11 12 13 these gyres are the dominant oceanic features of wind driven circulation and as such they reflect changes in climate and are a significant control on nutrient cycling and possibly atmospheric co2 concentrations here we present cd ca ratios in the shells of benthic foraminifera from the bahama banks that confirm previous suggestions11 12 that nutrient concentrations in the north atlantic subtropical gyre were much lower during the last glacial maximum than they are today up to 50 lower according to our data these contrasting nutrient burdens imply much shorter residence times for waters within the thermocline of the last glacial maximum below the glacial thermocline nutrient concentrations were reduced owing to the presence of glacial north atlantic intermediate water a high resolution cd ca record from an intermediate depth indicates decreased nutrient concentrations during the younger dryas interval as well mirroring opposite changes at a nearby deep site3 9 together these observations suggest that the formation of deep and intermediate waters north atlantic deep water and glacial north atlantic intermediate water respectively wax and wane alternately on both orbital and millennial timescales

further evidence for inclination shallowing in red beds red beds and related shallow marine siliciclastic sediments within the extensional catalan neogene basins offer a unique opportunity to study the relationship between sediment anisotropy remanence acquisition and inclination shallowing on the basis of the dominant fabric features sedimentary facies are grouped into laminated massive and bioturbated the bulk susceptibility appears to be dominated by paramagnetic phyllosilicates and clay minerals the magnetic susceptibility fabric is dominantly foliated while the degree of anisotropy is very variable and is dependent on the facies type strong foliation dominates in the laminated sediments whereas weak anisotropy characterizes the bioturbated and massive mass flow facies moreover we observe a correlation between facies type and remanence inclination the undisrupted thinly laminated facies provides the most biased inclination values 20 as opposed to 60 of the expected geomagnetic field steeper inclinations are reported from bioturbated muds while the best record of the geomagnetic inclination is found in the weakly anisotropic mass flow deposits

palaeomagnetic rotations in opposite senses in southeastern spain 20 volcanic and 3 sedimentary sites of upper miocene age were sampled in the cabo de gata region in southeastern spain palaeomagnetic and rockmagnetic investigations yielded useful results in 15 volcanic and 1 sedimentary site clockwise and anticlockwise block rotations of adjacent blocks could be observed the age of these rotations is younger than tortonian deformation in the eastern part of the betics seems to follow a different pattern than in the central and western part of the subbetic this behaviour can be related to the crustal structure in the eastern betics

late cretaceous paleomagnetic results from southeastern china and their geological implication abstract a paleomagnetic study was carried out on late cretaceous red beds in central jiangxi province southeastern china stepwise thermal demagnetization was used to isolate the characteristic higher temperature component htc from the jishui d 355 7 i 34 8 95 6 3 and ganzhou d 15 6 i 35 6 95 5 5 areas respectively the htc direction from the jishui area passes enkin s fold test at 95 confidence level and indicates an 18 9 5 5 counter clockwise rotation relative to the referent pole of the stable south china block scb the htc direction from ganzhou passes both mcfadden s fold test at 95 confidence level and reversal test comparing these two new poles 81 0 n 322 2 e a95 5 8 from jishui and 74 4 n 225 1 e a95 5 2 from ganzhou with other coeval poles reported from south china these results demonstrate a significant difference in paleolatitude 9 9 4 1 between coastal and inland areas which might be either related to dextral shearing faulting between them or inclination shallowing conducted by sedimentation and or compaction however results obtained from both anisotropy of the isothermal remanence air method and corrected results of the elongation inclination model of tauxe and kent l tauxe d v kent a simplified statistical modal for the geomagnetic field and the detection of shallow bias in paleomagnetic inclinations was the ancient magnetic field dipolar in j e t channell d v kent w lowrie j meert eds timescales of the paleomagnetic field geophys monogr am geophys union 145 2004 101 115 indicate that a distinct inclination flattening occurred in our samples

uptake of cadmium into calcite shells by planktonic foraminifera abstract planktonic foraminifera were cultured in the laboratory and the uptake of cd into their calcite investigated using cd and sr radiotracers best estimates of the effective distribution coefficient of cd relative to ca in planktonic foraminiferal calcite are 2 4 from these experiments and previously determined values of the sr distribution coefficient within the uncertainty of these estimates planktonic foraminiferal shells reflect seawater cd ca ratios with a proportionality constant similar to that determined for benthic foraminifera cd ca ratios in planktonic and benthic foraminiferal shells from sediment cores may be useful therefore for reconstructing water column profiles of cd ca over time

hydrological flowpaths and nitrate removal rates within a riparian floodplain along a fourth order stream in brittany france three main reservoirs were identified that contribute to the shallow subsurface flow regime of a valley drained by a fourth order stream in brittany western france i an upland flow that supplied a wetland area mainly during the high water period it has high n no3 and average cl concentrations ii a deep confined aquifer characterized by low nitrate and low chloride concentrations that supplied the floodplain via flow upwelling iii an unconfined aquifer under the riparian zone with high cl and low n no3 concentrations where biological processes removed groundwater nitrate this aquifer collected the upland flow and supplied a relict channel that controlled drainage from the whole riparian zone patterns of n no3 and cl concentrations along riparian transects together with calculated high nitrate removal indicate that removal occurred mainly at the hillslope riparian zone interface i e first few metres of wetland whereas dilution occurred in lower parts of the transects especially during low water periods and at the beginning of recharge periods stream flow was modelled as a mixture of water from the three reservoirs an estimation of these contributions revealed that the deep aquifer contribution to stream flow averaged 37 throughout the study period while the contribution of the unconfined reservoir below the riparian zone and hillslope flow was more variable from ca 6 to 85 relative to rainfall events and the level of the riparian water table at the entire riparian zone scale no3 removal probably from denitrification appeared most effective in winter despite higher estimated upland no3 fluxes entering the riparian zone during this period copyright 2003 john wiley sons ltd

magnetic inclination shallowing problem and the issue of eurasia s rigidity insights following a palaeomagnetic study of upper cretaceous basalts and redbeds from se china

correlation of nitrate profiles with groundwater and sediment characteristics in a shallow sandy aquifer abstract sediment profiles of a shallow sandy aquifer in an agricultural area of denmark can be characterized by a new term called total reduction capacity trc quantifying the total amount of reduced compounds in the aquifer material ferrous iron reduced sulfur compounds solid organic carbon a distinct increase of trc was observed at and below the oxidation reduction front in this study the front was a zone 30 cm wide oxygen nitrate and sulfate were present above the oxidation reduction front but disappeared at the front detailed porewater profiles indicate that denitrification also takes place above the front supposedly in anaerobic microenvironments not evident in the water samples from the small wells the trc profiles showed that some reduction capacity is still present above the oxidation reduction front and is apparently able to support denitrification

anomalously shallow inclination in middle northern part of the south china block palaeomagnetic study of late cretaceous red beds from yichang area summary we present new palaeomagnetic results from late cretaceous red beds of the paomagang formation collected at 42 sites in the yichang area 30 7 n 111 7 e middle northern part of the south china block a high unblocking temperature component around 680 c was isolated from 26 sites by stepwise thermal demagnetization fold tests are positive at the 95 per cent confidence limit for 14 and 11 sites of the paomagang and wangdian areas respectively normal and reversed polarity sequence found in the wangdian area passed a reversal test at the 95 per cent confidence limit the tilt corrected mean direction for yichang area is d 3 8 i 23 3 95 5 1 n 26 corresponding to a palaeopole at 71 5 n 280 0 e with a95 4 3 comparison with the expected inclination from the 80 ma eurasian apwp pole indicates a inclination flattening of 26 3 6 4 middle cretaceous to cenozoic nw se extension tectonics within the scb contributes only 2 0 to the inclination flattening while the massive samples of the paomagang formation show a moderate degree of anisotropy 1 017 pj 1 086 and steeper inclination i 29 3 the laminated samples which form more than 75 per cent of the studied samples show a higher degree of anisotropy 1 052 pj 1 227 and shallower inclination value i 22 7 a good correlation between remanence inclination and facies types indicates that depositional processes produced the observed shallow inclination in the yichang area

deep thermohaline circulation in the low latitude atlantic during the last glacial present day low latitude eastern and western atlantic basins are geochemically distinct below the sill depth of the mid atlantic ridge while antarctic bottom water aabw circulates freely in the western atlantic flow into the eastern atlantic is restricted below 4 km which results in filling the abyssal depths of this basin with water of geochemical similarity to nutrient depleted north atlantic deep water using carbon isotopes and cd ca ratios in benthic foraminifera we reconstruct the geochemistry of these basins during the last glacial maximum results indicate that deep eastern and western atlantic basins became geochemically identical during the last glacial this was achieved by shoaling of the upper surface of aabw above the sill depth of the mid atlantic ridge which allowed bottom waters in both basins to be filled with the same water mass although aabw became the dominant water mass in the deep eastern atlantic basin during the glacial holocene glacial 13c po4 shifts in this basin are in redfield proportions unlike the disproportionate holocene glacial 13c po4 shifts observed in the southern ocean by examining the composition of deep and intermediate waters throughout the atlantic we show that this effect was induced by a change in gradient of the 13c po4 deepwater mixing line during glacial times evidence from high latitude planktonic data suggests that the change in gradient of the deepwater mixing line was brought about through a significant reduction in the thermodynamic effect on southern ocean surface waters by using coupled 13c po4 data to constrain the composition of end member water masses in the glacial atlantic we conclude that deep waters in the low latitude glacial atlantic were composed of a mixture of northern and southern source waters in a ratio of 1 3

magnetostratigraphy of miocene pliocene zagros foreland deposits in the front of the push e kush arc lurestan province iran abstract the timing of the deformation in the zagros simply folded belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences the foreland basin infill at the front of the push e kush arc is composed of fine grained fluvial plain deposits agha jari fm and coarse conglomerates at the top of the section bakhtyari fm a magnetostratigraphic study was carried out in a composite section spanning about 2800 m in order to date growth strata and to constrain the timing of the deformation in the mountain front flexure mff magnetostratigraphic correlation of the base of the agha jari fm with chron c5a yields an age of 12 8 to 12 3 ma for this base the transition to the conglomerates of the bakhtyari fm correlates with the upper gauss chron c2an at approximately 3 ma the deposition age of the top of the preserved bakhtyari fm is extrapolated around the pliocene pleistocene boundary the base of the agha jari fm growth strata and thus the beginning of the deformation in the front of the push e kush arc is dated at 8 1 7 2 ma the topmost preserved bakhtyari is folded in the ne flank of the changuleh anticline and is unconformably overlying the sw flank of the anaran anticline this indicates that the tectonic deformation in the front of the push e kush arc was active at least during 5 my the mff is a relatively long lived structure active from 8 1 to 7 2 ma to about the pliocene pleistocene boundary partly synchronous with the changuleh anticline to the foreland after mff tectonic cessation only the changuleh anticline remained active

propagating and incorporating the error in anisotropy based inclination corrections summary sedimentary rock palaeomagnetic inclinations that are too shallow with respect to the ambient field inclination may be restored using anisotropy based inclination corrections or techniques that rely on models of the past geomagnetic field one advantage of the anisotropy technique is that it relies on measured parameters declinations inclinations bulk rock magnetic fabrics and particle magnetic anisotropy that have measurement errors associated with them rather than relying on a geomagnetic field model and statistical treatment of the data sofar however theerrorassociatedwiththemeasurementshasnotbeenpropagatedthrough the corrections and the reported uncertainties are simply the 95 95 per cent confidence circles of the corrected directions in this paper we outline different methodologies of propagating the error using bootstrap statistics and analytic approximations using the case example of the shepody formation inclinationcorrection bothtechniquesareingoodagreementandindicateamoderate 15per cent uncertainty in the determination of the flattening factor f used in the correction such uncertainty corresponds to an 0 31 increase of the confidence cone and a bias that steepens the mean inclination by 0 32 for other haematite bearing formations realistic uncertainties for f ranging from 0 and 30 per cent were used together with an intermediate value of 15 per cent yielding a maximum expected increase in the confidence cones and steepening of the inclinationsof 1 suchresultsindicatethatformoderateerrorsoff theinclinationcorrection itself does not substantially alter the uncertainty of a typical palaeomagnetic study we also compare the uncertainties resulting from anisotropy based corrections to those resulting from the elongation inclination e i technique uncertainties are comparable for studies with a large sample number 100 otherwise the anisotropy based technique gives smaller uncertainties whenanisotropydataarenotavailable itispossibletoestimateacorrectionusingflattening factors f obtained from the literature a range of flattening factors has been observed for both magnetite and haematite bearing rocks 0 4 f 1 for haematite and 0 54 f 1f or magnetite but the exact value is specific to the anisotropy of the formation to evaluate the maximum effects of inclination shallowing the smallest f for magnetite or haematite should be used

compaction induced inclination shallowing in synthetic and natural clay rich sediments experiments using single clay slurries consisting of acicular or equidimensional magnetite mixed with either kaolinite illite montmorillonite or chlorite were conducted to determine the effect of compaction on inclination a natural marine sediment and a reconstructed marine sediment made up of the clays used in our single clay experiments were also studied a laboratory postdepositional remanence imparted to the slurries by stirring had its inclination shallowed by compaction for both the single clay samples as seen previously anson and kodama 1987 and the natural and reconstructed marine sediments suggesting that our single clay sediments are valid analogues of natural sediments magnetic intensity also decreased by 30 50 during compaction the greatest decrease occurring for samples with the steepest initial inclination altering the ph of a slurry so that the magnetite would have a negative surface charge and be repelled by clay particles did not affect a slurry s inclination shallowing behavior suggesting that electrostatic attraction between magnetite and clay is probably not a major contributor to inclination shallowing however most of the inclination shallowing observed in our experiments occurs at low pressures when void ratios are high comparison with a clay microfabric compaction study mcconnachie 1974 suggests that volume loss at these pressures is accommodated by reorientation of clay particles or clay particle aggregates clay domains since pore spaces are large at these low pressures inclination shallowing is probably caused by magnetite particles either being attached to clay particles perhaps by van der waals forces or having been incorporated into clay domains alternating field demagnetization of compacted samples which contain magnetite with a range in grain sizes supports this model indicating that the smallest magnetic grains are slightly more shallowed by compaction than larger grains our results suggest that a sediment s clay content may be an important contributor to inclination shallowing

laboratory depositional and compaction caused inclination errors carried by haematite and their implications in identifying inclination error of natural remanence in red beds summary undetected depositional and or compaction caused inclination errors may result in an overestimation of tectonically caused latitudinal offset hodych buchan used a single component isothermal remanent magnetization irm acquired in a dc field at a 45 angle to the bedding to test for inclination errors in silurian red beds this approach was criticized by stamatakos et al we produced synthetic depositional and compaction caused inclination errors to test hodych and buchan s approach red bed samples collected from the eocene suweiyi formation tarim basin northwest china were disaggregated using an ultrasonic cleaner and the sediments were mixed with distilled water to make a sediment slurry the sediment slurry spontaneously separated into silt dominated and clay sized parts so deposition and compaction experiments were conducted with three categories of slurries coarse grained the fine grained and a 1 1 volume ratio mixture of the coarse and fine grained slurries during compaction clay sized sediments experienced 17 19 inclination shallowing at 58 magnetic field inclination while coarser sediments showed little laboratory compaction caused inclination error acquisition of irm coercivity spectra and unblocking temperature spectra reveal that the magnetic carrier for the fine grained sample is dominated by pigmentary haematite a deposition experiment was also conducted with the coarse grained sediments which showed a range of depositional inclination error 0 30 carried by larger high unblocking temperature coercivity particles the intermediate unblocking temperature or coercivity component carried presumably by pigmentary haematite is an accurate record of the ambient magnetic field direction our data indicate that the single component irm method of hodych buchan can be used to identify and correct for the compaction caused inclination error of the fine grained samples while it failed to detect any depositional inclination error in the coarse grained samples therefore to better quantify the inclination error in red beds it is suggested that multiple irms be measured in various directions

paired benthic foraminiferal cd ca and zn ca evidence for a greatly increased presence of southern ocean water in the glacial north atlantic benthic foraminiferal 13c and cd ca studies suggest that deep atlantic circulation during the last glacial maximum was very different from today with high nutrient low 13c high cd deep southern ocean water sow penetrating far into the north atlantic however if some glacial 13c values are biased by productivity artifacts and or air sea exchange processes then the existing 13c data may be consistent with the continual dominance of north atlantic deep water nadw cibicidoides wuellerstorfi cd ca results presented here indicate that the glacial north atlantic was strongly enriched in dissolved cd below 2500 m depth if nadw formation was still vigorous relative to sow formation these data could be explained by either increased preformed nutrient levels in the high latitude north atlantic or by increased organic matter remineralization within lower nadw high glacial zn ca values in the same samples however are best explained by a substantially increased mixing with zn rich sow the cause was most likely a partial replacement of nadw by less dense glacial north atlantic intermediate water this reorganization also lowered deep north atlantic co32 concentrations by perhaps 10 to 15 mol kg 1

lack of a significant temperature influence on the incorporation of cd into benthic foraminiferal tests 1 benthic foraminiferal cd ca is an important proxy for seawater paleonutrient concentrations and therefore deep ocean paleocirculation although previous work suggests that the incorporation of cd into benthic foraminiferal calcite is insensitive to temperature at least one species of planktonic foraminifer appears to be strongly influenced the present study provides a closer look at the relationship between benthic cd partition coefficients and temperature using new and previously published data from the bahama banks neither calcitic taxa nor the aragonitic hoeglundina elegans exhibits any consistent changes in partition coefficients over the range 4 to 18 c

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

compaction and inclination shallowing in deep sea sediments from the pacific ocean progressive downcore shallowing of the remanent inclination has been observed in a 120 m section of marine sediments at deep sea drilling project site 578 in the northwest pacific representing the past 6 5 m y near the top of the section the average inclination corresponds to the expected geocentric axial dipole value of 53 but shallows down section by about 6 to 8 northward translation of the pacific plate accounts for only about a quarter of the inclination shallowing moreover no inclination shallowing was observed at neighboring site 576 which has considerably lower sedimentation rates and the last 5 m y are represented by a 26 m sedimentary section we correlate the inclination shallowing at site 578 with an average decrease in porosity of 3 4 the porosities in the top 26 m at site 576 are slightly higher than at site 578 and show no definite trend downhole we interpret these results to suggest that both the downhole inclination shallowing and decrease of porosity in site 578 are caused by sediment compaction compaction does not play a significant role for the section at site 576 due to its much shorter length

palaeomagnetism and magnetic anisotropy of carboniferous red beds from the maritime provinces of canada evidence for shallow palaeomagnetic inclinations and implications for north american apparent polar wander summary a palaeomagnetic and magnetic anisotropy study was conducted on the lower middle carboniferous maringouin and shepody red bed formations of the maritime provinces of canada to detect and correct inclination shallowing because of the shallow inclinations commonly observed in red beds and the strong dependence of north america s palaeo mesozoic apparent polar wander apw on red beds inclination shallowing may substantially affect large portions of north america s apw path hematite is the primary magnetic mineral carrier in these red beds accompanied by secondary magnetite maghemite goethite and pigmentary hematite thermal and chemical demagnetization of the shepody fm successfully isolated characteristic remanence directions of d 177 i 20 4 95 6 5 n 19 and d 177 8 i 17 7 95 6 9 n 16 respectively thermal demagnetization of the maringouin fm isolated a characteristic remanence direction of d 178 7 i 24 9 95 14 5 n 9 high field anisotropy of isothermal remanence followed by alternating field and thermal cleaning on leached samples was used to isolate the fabric of hematite individual particle anisotropy was measured directly from magnetic separates using a new technique hematite s magnetic fabric and particle anisotropy were used to apply an inclination correction our inclination corrections indicate up to 10 of inclination shallowing corresponding to corrected palaeopole positions of 27 2 n 118 3 e a95 6 2 and 27 4 n 117 2 e a95 13 1 for the shepody and maringouin formations respectively this correction corresponds to a 6 increase in colatitude for carboniferous north america which translates into approximately a 650 km change in north america s palaeogeographic position the proposed position of north america supports a pangea b type reconstruction

a geostrophic transport estimate for the florida current from the oxygen isotope composition of benthic foraminifera we present a new method for the quantitative reconstruction of upper ocean flows for during times in the past for the warm t 5 c surface ocean density can be accurately reconstructed from calcite precipitated in equilibrium with seawater as both of these properties increase with decreasing temperature and increasing salinity vertical density profiles can be reconstructed from the oxygen isotopic composition of benthic foraminifera the net volume transport between two vertical density profiles can be calculated using the geostrophic method using benthic foraminifera from surface sediment samples from either side of the florida straits florida keys and little bahama bank we reconstruct two vertical density profiles and calculate a volume transport of 32 sv using this method this agrees well with estimates from physical oceanographic methods of 30 32 sv for the mean annual volume transport we explore the sensitivity of this technique to various changes in the relationship between temperature and salinity as well as salinity and the oxygen isotopic composition of seawater

tectonic elements with south china affinity in the korean peninsula new early jurassic palaeomagnetic data summary early jurassic sandstones and shales were collected at 14 sites from the kimpo area in the western part of the korean peninsula for a palaeomagnetic study a characteristic remanent magnetization component which passes the fold test was isolated from seven sites this characteristic component is interpreted to be of primary early jurassic origin because the folding age is middle late jurassic the primary directions together with previously reported ones provide a mean direction d 38 1 i 39 7 95 3 8 11 sites and a palaeomagnetic pole 54 1 n 230 2 e a95 4 1 for the kimpo area this palaeomagnetic pole shows good agreement with the coeval poles for the south china block and is significantly removed from that for the north china block suggesting that the kimpo area has been part of the south china block since at least early jurassic times the kimpo area constitutes a part of the imjingang belt which is palaeontologically allocated to the south china block in its origin while all precambrian tectonic blocks that compose the basement of the korean peninsula are interpreted to be of north china origin we conclude that the imjingang belt including the kimpo area is a tectonic extension of the south china block on the korean peninsula the south china elements were obducted onto the north china block at the site of the present korean peninsula during the collision event of the north and south china blocks and hence the korean peninsula is composed of areas with both north and south china affinities

palaeogeographic implications of differential inclination shallowing in permo carboniferous sediments from the donets basin ukraine abstract we present new palaeomagnetic data from upper carboniferous and lower permian grey and red sediments from the donets basin ukraine part of the palaeozoic east european platform detailed demagnetization of these units reveals two ancient components of magnetization component b which is carried by magnetite and pigmentary haematite and a high unblocking temperature component c present only in the red beds carried by detrital haematite the b and c components both pass fold tests indicating a primary or a near primary origin for magnetizations the c component however yields palaeolatiudes that are consistently lower by up to 12 of latitude or 1330 km than those derived from the b component and we argue that this is due to significant inclination shallowing of the c component a comparison with european reference palaeomagnetic data reveals that the reference data also span a large spread of palaeolatitudes for this time and we argue that unrecognized shallowing may have crept into the reference data when based on sedimentary units a more rigorous approach to selecting reference palaeomagnetic data may well be key to resolving palaeogeographic controversies at this time

magnetostratigraphy of the vallesian late miocene in the valles penedes basin northeast spain the magnetostratigraphic analysis of the late miocene continental deposits from the valles penedes basin combined with its well documented fossil mammal record has provided a well resolved chronology for the upper basin infill the study is based on the biostratigraphic and magnetostratigraphic cross correlation of 12 sections throughout the alluvial sequences in the western valles area the biostratigraphic framework consists of 21 mammal localities corresponding to the mammal neogene mn9 and mn10 units the composite magnetic polarity sequence is based on 400 paleomagnetic sites correlation with the geomagnetic polarity time scale gpts has led to an absolute dating of the faunal events and a precise chronostratigraphy of the vallesian mammal stage in its type area the hipparion first appearance datum fad at the mn8mn9 boundary is dated at 11 1 ma in the valles penedes basin this age compared to other radiometrically dated localities in europe north africa and turkey is consistent with an isochronous dispersal of this equid through the mediterranean region a possible isochrony at a larger geographical scale old world mesogea must await more reliable ages of the hipparion fad in asia and africa the cricetulodon fad mn9amn9b boundary is dated to 10 4 ma in chron c5n the progonomys fad mn9mn10 boundary corresponding to the intra vallesian faunal crisis is dated at 9 7 ma c4ar 3r the vallesian spans 2 4 myr from 11 1 ma c5r 1n to 8 7 ma c4an and correlates to the early tortonian

magnetic anisotropy as a correction for compaction caused palaeomagnetic inclination shallowing summary a theoretical model presented by jackson et al 1991 suggests that the anisotropy of anhysteretic remanence aar can be used to recognize and correct for compaction caused inclination shallowing in sediments and sedimentary rocks however we have conducted experiments in which inclination shallowing is more strongly dependent on magnetic anisotropy during compaction of synthetic clay rich sediments containing 0 45 m acicular magnetite than predicted by the jackson et al model this discrepancy can be explained if randomization or disturbance of subvertical magnetite particles is the cause of inclination shallowing early in the compaction process the principal experimental evidence for this effect is a decrease in magnetization intensity coincident with inclination shallowing an intensity decrease during inclination shallowing is also observed in some dsdp cores suggesting that this randomization process may also occur in nature after randomization magnetite particles become firmly attached to clay particles and both magnetic anisotropy and inclination shallowing show a regular increase during compaction consistent with the jackson et al model we suggest that models like that of jackson et al can be used to correct for inclination shallowing if they are used in conjunction with an experimentally derived relationship between inclination shallowing and magnetic anisotropy for a particular sediment

the vallesian mammal succession in the valles penedes basin northeast spain paleomagnetic calibration and correlation with global events abstract the integrated lithostratigraphic biostratigraphic and magnetostratigraphic study of new and classical alluvial fan sequences in the valles penedes basin northeast spain western mediterranean enabled a considerable refinement of the vallesian mammalian succession in this basin and its correlation with the magnetic polarity time scale up to 12 new sections were logged and sampled in a search of mammal remains and a paleomagnetic analysis was carried out the correlation among these sections was based on the small mammal content and the succession of magnetozones enabling the establishment of four main composite sections les fonts montagut terrassa and viladecavalls as a result the vallesian in the valles penedes basin appears punctuated by four main mammalian events which coincide with the appearance of the genera hipparion cricetulodon progonomys and rotundomys the hipparion event did not coincide with any further change in the associations of small and large mammals the dispersal of the cricetid cricetulodon in its turn involved the first set of extinctions in the vallesian affecting the rodent and carnivore and artiodactyl associations the main break during the vallesian coincided with the dispersal of the murids of the genus progonomys and implied a sudden drop in the diversity of the rodent and artiodactyl species of warm wet forested affinities this phase is characterized by the association of the murid progonomys and the cricetid cricetulodon and includes the last record of hominoids in the basin the replacement of cricetulodon by the sigmodont cricetid rotundomys was associated with the entry of some typical early turolian species according to the correlation established it is concluded that the fad of hipparion in the valles penedes basin is dated at 11 1 ma at the base of chron c5r 1n this data is congruent with other datings in northern africa and eastern europe suggesting the isochrony of this event in the mediterranean regions the cricetulodon fad is dated to 10 4 ma in chron c5n the progonomys dispersal coincident with the late vallesian crisis is dated at 9 7 ma in chron c4ar 3r the rotundomys fad is dated at 9 2 9 3 ma in the upper part of chron c4ar 1n the vallesian mammal bioevents affected the peri mediterranean zones including northern africa and other regions in northern and western eurasia these paleofaunistic changes were caused by temperature descent from subtropical to warm temperate conditions as well as by changes in the aridity balance and seasonality this climatic evolution was the result of the interplay of diverse global events cooling of the high latitude regions growing of the antarctica ice sheet and enhancement of the thermohaline oceanic circulation and of large scale tectonic and paleogeographic processes surface uplift of the himalayas the tibetan plateau and other tectonic reliefs closing of gateways between the mediterranean marine regions and the world ocean the magnetobiochronology resulting from the study of the western valles sequences suggests a close chronological correlation between some of these global and regional processes and the vallesian bioevents recorded

acquisition of detrital magnetization in four turbidites turbiditic events are mostly avoided in paleomagnetic studies and therefore their remanence and magnetic properties are poorly described turbidites are exempt of bioturbation and potentially provide pertinent information about depositional remanence we studied four quaternary turbidites of different origins in marine sediment cores upward fining of both magnetic and sedimentary fractions indicates that coarser grains reached the bottom first we observe a progressive shallowing of the magnetic inclinations between the upper and bottom layers of the turbidites that increases with the size of the events and obeys a simple linear scaling law measurements of magnetic anisotropy suggest that hydrodynamic conditions prevailing during deposition seem to be dominant for the alignment of the magnetic grains we suggest that small spherical grains are randomly oriented with zero resultant magnetization in presence of strong turbulent conditions while the alignment of elongated grains is constrained by the competition between gravity and magnetic forces a possible scenario is that under turbulent conditions they tend to rest at the bottom with their long axes parallel to the sediment surface and therefore with shallow inclinations whereas weakly turbulent conditions like during the smallest 26 cm thick event do not disturb the magnetic alignment and therefore do not generate inclination shallowing this article is protected by copyright all rights reserved

an analytical solution for correcting palaeomagnetic inclination error summary with increasing evidence showing significant inclination shallowing in red beds it is important to develop useful tools to detecting and correcting inclination errors for haematite bearing sedimentary rocks theoretically any deviation of magnetization from the ambient magnetic field can be described by a preferred orientation distribution od of unique axes of the anisotropic magnetic particles based on stephenson s continuous particle od function magnetic anisotropy parameters of a bulk sample and inclination correction equations were derived considering all the magnetic particles in a sample in addition to our new equations for correcting red bed inclination error the results also confirm the inclination correction of jackson et al for magnetite bearing samples which is based on a simple discrete particle od model used by stephenson et al to show their derivations suggesting that the inclination correction is probably independent of the particle od models

paleomagnetism of fluorite veins in the devonian st lawrence granite newfoundland canada paleomagnetic results are reported from the devonian st lawrence granite and the fluorite veins within the granite or its related porphyry dikes paleomagnetic analysis of 359 specimens from 29 sites shows that there is no statistically significant difference at 95 confidence between the site mean characteristic remanent magnetization chrm directions carried by pyrrhotite and or magnetite of the granite and fluorite veins no post granite metamorphic event is known in the area thus these concordant directions indicate that the granite and fluorite veins are coeval and retain a primary remanence however the mean chrm direction of 25 vein and granite sites yields an early pennsylvanian paleopole of 316 ma on the north american apparent polar wander path at 35 5 n 129 2 e a95 3 4 that is younger than the 374 2 ma devonian u pb zircon age for the granite two intersecting vertical vein sets indicate that the st lawrence granite has not been tilted since emplacement of the fluorite veins t

evidence for weak ferromagnetic moment within the basal plane of hematite natural crystals at low temperature 1 low temperature magnetization of hematite within the basal plane has been studied in a collection of natural crystals by means of torque magnetometry comparison between the torque curves at room temperature and at 77 k allows identification of a weak ferromagnetic moment constrained within the basal plane at temperatures well below the morin transition annealing the samples produces the expected reduction of the weak ferromagnetic moment but there is also a relationship between the ferromagnetic moment before and after annealing low temperature measurements after the annealing experiment reveal the presence of a weak ferromagnetic moment that survives the annealing this observation suggests the magnetic structure of natural hematite crystals below the morin transition can still be a carrier of magnetization

tectonic implications of early middle triassic palaeomagnetic results from hexi corridor north china summary a palaeomagnetic study was carried out on low middle triassic red beds at jingtai area of hexi corridor the characteristic higher temperature component htc ds 304 1 is 38 4 ks 33 2 a95 5 2 n 24 sites isolated by stepwise thermal demagnetization exhibits dual polarity which passes the mcfadden s fold test at the 99 per cent confidence level and reversal test with classification c compared with coeval palaeomagnetic results from the north china block ncb this result suggests insignificant palaeolatitude differences p between the observed and that expected at jingtai area p 0 9 4 9 in the early triassic or p 4 9 4 1 in the middle triassic this implies that the hexi corridor was the extension of the ncb by the middle triassic however in comparison with early and middle triassic results from the ncb an anticlockwise rotation of studied area relative to the ncb with rd 25 4 5 2 or rd 26 6 4 5 is detected our result also suggests that jingtai area of the western part of ncb was not connected with the tarim block by the early middle triassic

evolution of the central catalan margin of the valencia trough western mediterranean abstract the evolution of the central catalan margin was conditioned by major fault activity and thermal processes generated by crustal thinning the continental margin structure is characterised by major ne sw striking southeast dipping basement faults which have given rise to a graben half graben and horst system these faults acted essentially as normal faults no major neogene strike slip activity has affected the continental margin although minor episodic variations from the dominant extensional regime to strike slip tectonics cannot be discounted two major structural evolutionary stages took place at the margin the transition from one stage to the other being gradual 1 rifting stage late oligocene to early burdigalian related to the opening of the valencia trough and from which originated both the barcelona and valles penedes half grabens 2 thermal subsidence stage late burdigalian to present generated by the subsequent crustal cooling and thinning fault activity during this stage was essentially concentrated in the major half graben bounding faults the sedimentary evolution of the central sector of the catalan margin was controlled by the tectonic and crustal evolution as well as by the successive sea level and paleoclimatic changes which affected the region drastic changes in the depositional systems took place during the transition from the rifting stage into the thermal subsidence stage during aquitanian langhian time characterized by an overall trend of pulsating encroachment of marine conditions over the continental margin a noticeable diversity of depositional systems alluvial lacustrine coastal evaporitic fan delta bay shelf carbonate platform systems developed from the latest serravallian up to the present the depositional framework was less varied due to a general lowering of sea level and to the final onlapping of most of older structural highs which are now buried below the miocene sediments two progradational terrigenous shelf talus systems separated by the messinian erosive surface developed during the latest serravallian tortonian and pliocene quaternary

detrital remanence inclination errors and anhysteretic remanence anisotropy quantitative model and experimental results summary we suggest that inclination errors in detrital remanent magnetization drm may be recognized and corrected by measurement of the anisotropy of anhysteretic remanent magnetization arm arm anisotropy reflects directional variations in the remanence capacity of relatively fine grained magnetic particles in rocks or sediments generally the same particles that carry the stable component of drm relative vertical and horizontal drm magnitudes are controlled by this directional remanence capacity as well as by the alignment efficiency of the particle magnetic moments which in turn is governed by the relative intensities of the vertical and horizontal components of the ambient magnetic field thus the respective vertical and horizontal components of palaeointensity and therefore palaeofield inclination may be obtained by normalizing the measured drm components by parallel arm intensities synthetic sediments containing silica kaolin and sized magnetite powders have previously been found to acquire experimental drm with an inclination error that is a direct function of kaolin concentration further experiments have now shown that arm anisotropy in the synthetic sediments is also a direct function of kaolin content and thus a correlation exists between drm inclination errors and arm anisotropy multiplying the measured drm vector by the inverse of the arm anisotropy matrix yields an improved estimate of the actual laboratory depositional field in all cases for samples with acicular 0 5 m magnetite this procedure reduces a mean inclination error of over 5 to less than 0 5 samples with subequant magnetite of slightly larger grain size 0 75 m exhibit similar arm anisotropy 10 per cent but somewhat larger inclination errors 10 we interpret this in terms of stronger horizontal alignment but weaker particle anisotropies for the larger more equant magnetites

tectonic deformation of the southwestern part of the yangtze craton inferred from paleomagnetism abstract upper cretaceous red sandstones have been sampled at 21 sites from the jiangdihe formation in yuanmou 25 9 n 101 7 e the northern part of yunnan china characteristic directions with unblocking temperature of 680 c have been isolated from all the sites and provide a positive fold test which is significant at the 99 probability level remanent magnetization of the prefolding origin represents a characteristic direction of the jiangdihe formation d 26 9 i 35 6 and 95 3 6 this paleomagnetic direction confirms the fairly large easterly declination of the cretaceous time for the southern part of the yangtze craton incorporating this result into previous data from the areas along the longitude of 102 e in the southwestern part of yangtze craton the declination value in the cretaceous paleomagnetic direction monotonously decreases from 45 to 2 as latitude increases from 25 0 to 30 1 n the tectonic rotation expected from the apparent polar wander path of eurasia shows that the clockwise rotation decreases gradually from 30 to 10 whilst increasing in latitude the systematically differential rotation along the longitude in the southwestern part of the yangtze craton is a part of the deformation mode of the asian continent due to the collision with india the yangtze craton behaved as a unit continuum material with a ductile nature during deformation

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

internal crustal deformation in the northern part of shan thai block new evidence from paleomagnetic results of cretaceous and paleogene redbeds in order to describe the internal deformation of the northeast part of the shan thai block resulting from the penetration of the indian plate into asia a paleomagnetic study was carried out on the cretaceous and paleogene strata in the southern part of the simao terrane high temperature magnetic components with unblocking temperatures around 680 degrees c were isolated and positive fold test shows its primary nature of magnetization the tilt corrected site mean directions of the lower cretaceous and upper cretaceous from the menglun area are d s 46 2 degrees i s 45 9 degrees k 11 0 alpha 95 10 6 degrees and d s 33 2 degrees i s 30 9 degrees k 68 4 alpha 95 8 2 degrees respectively the site mean directions of the upper cretaceous and lower paleogene for the mengban area are d s 50 5 degrees i s 31 0 degrees k 207 6 alpha 95 6 4 degrees and d s 43 5 degrees i s 23 0 degrees k 26 1 alpha 95 13 4 degrees respectively the results of the lower cretaceous and upper paleogene from the mengla area are d s 46 9 degrees i s 42 2 degrees k 27 3 alpha 95 7 7 degrees and d s 41 8 degrees i s 23 8 degrees k 38 9 degrees alpha 95 5 8 degrees respectively in comparison with previous paleomagnetic data of the simao terrane the rotational deformation can be divided into four stages the cretaceous and paleocene sediments of the simao terrane experienced intensive folding before the early oligocene during the early oligocene to early miocene the shan thai and indochina blocks experienced southeastward extrusion with similar to 20 degrees clockwise rotation relative to the south china block during the middle to late miocene the shan thai blocks experienced more 15 degrees clockwise rotation since the late miocene the activity of strike slip faults surrounding the simao terrane enhanced the internal differential rotations of the terrane these deformation processes finally resulted in a complex internal deformation of the simao terrane c 2013 elsevier b v all rights reserved

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

refinements of the european mammal biochronology from the magnetic polarity record of the plio pleistocene zujar section guadix baza basin se spain abstract the magnetobiostratigraphy study of the 130 m thick zujar section negratin clays unit guadix baza basin spain provides a remarkable opportunity to improve the correlation of european mammal biostratigraphy to the geomagnetic polarity time scale the occurrence of 12 well defined magnetozones and four paleontological sites with diagnostic faunas ranging from the mn 15 biozone ruscinian to the mn 17 biozone villanyian leads to an unambiguous correlation to chrons spanning from the gilbert to the matuyama epochs this provides two new time constraints 1 the boundary between mn 15 ruscinian and mn 16 villanyian biozones is recorded between chron c2an 3n and the base of chron c2an 2n and 2 the boundary between the upper and lower mn 16 subzones villanyian is located between chron c2an 2n and the base of chron c2an 1n the correlation between the ruscinian villanyian boundary and the 3 3 myr b p cooling event seems to be confirmed while the early late villanyian boundary could be tentatively correlated to the glacial event at 2 6 myr b p furthermore mn 15 faunas are found in the lowermost part of chron c2ar which is in agreement with and reinforces the emplacement of the mn 14 mn 15 ruscinian zones boundary at the reversal from chron 3n 1n to chron c2ar

the cenozoic rotational extrusion of the chuan dian fragment new paleomagnetic results from paleogene red beds on the southeastern edge of the tibetan plateau abstract paleomagnetic studies were conducted on the eocene and oligocene strata at the western part of the chuan dian fragment in order to describe the crustal deformation induced by continuous penetration of the indian plate into eurasia during the late cenozoic high temperature magnetic components with unblocking temperatures of 680 c were isolated and positive fold and or reversal tests reveal the primary nature of the magnetization the tilt corrected site mean directions obtained from the oligocene and middle early eocene strata are respectively ds 200 9 is 31 3 k 52 8 95 7 7 and ds 29 7 is 32 0 k 44 9 95 5 6 comparison of these results with previous paleomagnetic data from the chuan dian fragment shows that the western and central parts of the chuan dian fragment experienced 20 integral clockwise rotation relative to east asia since the middle miocene however the eastern part of the chuan dian fragment has experienced different rotational deformation relative to east asia since the pliocene because of the intense regional crustal deformation and activity on fault systems the eastern boundary of the chuan dian fragment was bounded by the yuanmou luezhijiang left lateral strike slip fault prior to the pliocene and then substituted by the xiaojiang left lateral strike slip fault since the pliocene due to the eastwards spreading of the clockwise rotational movement of the chuan dian fragment the evolutionary characteristics of the ailaoshan red river and xianshuihe xiaojiang strike slip faults were controlled by the difference between the clockwise rotational extrusion velocities of the chuan dian fragment and the indochina block

on the origin of inclination shallowing in redeposited sediments we studied the detrital remanent magnetization of laboratory redeposited lake sediments previously shown to be excellent recorders of the paleomagnetic field the redeposited and original natural sediments have indistinguishable stabilities to alternating fields af demagnetization and remanence intensities indicating that their remanences reside in the same magnetic particles thermomagnetic behavior hysteresis parameters and relatively high af stabilities of the detrital and anhysteretic remanences are essentially identical throughout the sediment column suggesting uniform distributions of submicron magnetite grains the declination is accurately recorded but inclination shallowing averaging 18 o is observed for routinely hand stirred rapidly redeposited sediments however sonically disaggregated sediments settle more slowly with anomalous shallowing averaging 7 o decreasing upward in the redeposited column these results indicate that thorough disaggregation of the sediment reduces the magnitude of the inclination shallowing probably by more efficiently isolating the magnetic grains from the matrix thus diminishing the dominance of the gravitational over geomagnetic aligning torques during deposition the progressive decrease of the inclination shallowing upward in the sediment column might be due to a parallel upward increase in the fraction of isolated magnetic particles which undergo brownian motion and alignment by the geomagnetic field the dominance of gravitational over geomagnetic aligning torques during deposition might be a cause for inclination shallowing in some coarser sediments in contrast inclination shallowing would be minimized for slow deposition of isolated submicron magnetite grains during natural sedimentation

a biomineralization model for the incorporation of trace elements into foraminiferal calcium carbonate measurements of srca of benthic foraminifera show a linear decrease with water depth which is superimposed upon significant variability identified by analyses of individual foraminifera new data for cdca support previous work in defining a contrast between waters shallower and deeper than 2500 m measured element partition coefficients in foraminiferal calcium carbonate relative to sea water d have been described by means of a one box model in which elements are extracted by rayleigh distillation from a biomineralization reservoir that serves for calcification with a constant fractionation factor such that d 1 f 1 f where f is the proportion of ca remaining after precipitation a modification to the model recognises differences in element speciation the model is consistent with differences between dsr dba and dcd in benthic but not planktonic foraminifera depth variations in d for sr and ba are consistent with the model as are differences in depth variation of dcd in calcitic and aragonitic benthic foraminifera the shallower depth variations may reflect increasing calcification rates with increasing water depth to an optimum of about 2500 m observations of unusually lower dcd for some deep waters not accompanied by similar dsr or dba may be because of dissolution or a calcification response to a lower carbonate saturation state

sr ca in multiple species of planktonic foraminifera implications for reconstructions of seawater sr ca sr ca ratios were measured on eight species of planktonic foraminifera from a core top transect of the north atlantic five of the species globigerinoides ruber globigerina bulloides neogloboquadrina pachyderma globigerinoides sacculifer globigerinella siphonifera show remarkably little within species variability in sr ca 1 2 0 1 three globorotaliid species globorotalia hirsuta globorotalia inflata globorotalia truncatulinoides show somewhat greater variability 3 7 interspecies variations are of 10 the variability in globorotaliid sr ca is explained either by a greater temperature sensitivity than for other species or by depth dependent dissolution other than this effect the overwhelming control on foraminiferal sr ca appears to be seawater sr ca in contrast time series sr ca records of four species from a north atlantic sediment core over a glacial interglacial cycle show very significant differences n pachyderma shows large amplitude changes in sr ca 9 7 in phase with 18o whereas g ruber shows the smallest amplitude changes 2 6 out of phase with 18o and most similar to model predictions for temporal changes in seawater sr ca records of g inflata and g bulloides are intermediate amplitude changes of 3 3 4 7 and out of phase with 18o the lack of coherence in the time series records between the species shows that factors in additional to changing seawater sr ca must affect planktonic foraminiferal sr ca

nitrate in groundwater and water sources used by riparian trees in an agricultural watershed a chemical and isotopic investigation in southern minnesota this study evaluates processes that affect nitrate concentrations in groundwater beneath riparian zones in an agricultural watershed nitrate pathways in the upper 2 m of groundwater were investigated beneath wooded and grass shrub riparian zones next to cultivated fields because trees can be important components of the overall nitrate pathway in wooded riparian zones water sources used by riparian trees and possible effects of trees on nitrate concentrations in groundwater were also investigated average nitrate concentrations in shallow groundwater beneath the cultivated fields were 5 5 mg l upgradient of the wooded riparian zone and 3 5 mg l upgradient of the grass shrub zone shallow groundwater beneath the fields passed through the riparian zones and discharged into streams that had average nitrate concentrations of 8 5 mg l as n lateral variations of d values in groundwater showed that mixing among different water sources occurred beneath the riparian zones in the wooded riparian zone nitrate concentrations in shallow groundwater were diluted by upwelling nitrate poor deep groundwater upwelling deep groundwater contained ammonium with a 15n of 5 that upon nitrification and mixing with nitrate in shallow groundwater caused nitrate 15n values in shallow groundwater to decrease by as much as 19 5 stream water penetrated laterally beneath the wooded riparian zone as far as 19 m from the stream s edge and beneath the grass shrub zone as far as 27 m from the stream s edge nitrate concentrations in shallow groundwater immediately upgradient of where it mixed with stream water averaged 0 4 mg l in the wooded riparian zone and 0 8 mg l near the grass shrub riparian zone nitrate concentrations increased toward the streams because of mixing with nitrate rich stream water because nitrate concentrations were larger in stream water than shallow groundwater concentrated nitrate in the streams cannot have come from shallow groundwater at these sites water sources of riparian trees were identified by comparing d values of sap water soil water groundwater and stream water soil water was the main water source for trees in the outer 4 to 6 m of one part of the wooded riparian zone and outer 10 m of another part groundwater was a significant water source for trees closer to the streams where the water table was less than about 2 1 to 2 7 m below the surface no evidence was found in the nitrate concentration profiles that trees close to the streams that took up groundwater through their roots also took up nitrate from groundwater the lack of such evidence is attributed to the nitrate concentration profiles being insufficiently sensitive indicators of nitrate removal by trees

planktonic foraminiferal cd ca paleonutrients or paleotemperature records of cd ca in planktonic foraminiferal calcite of globigerinoides bulloides in cores from the subantarctic region of the southern ocean show large glacial interglacial variations with lower cd ca by 0 06 0 10 mol mol 1 at glacial times interpretation of these records in terms of lower dissolved phosphate and inferred higher glacial nutrient utilization has significant implications for glacial atmospheric carbon dioxide pco2 draw down however box core top data for g bulloides in the north atlantic suggest that the incorporation of cd into planktonic foraminifera relative to seawater dcd is temperature sensitive dcd 0 637 exp 0 15t when the subantarctic planktonic cd ca records are corrected for this temperature dependence they show little or no glacial interglacial diferences if as seems likely this observation can be interpreted to indicate a minimal change 0 5 mol kg 1 in surface water phosphate concentrations then the explanation for lowered glacial pco2 must be looked for elsewhere