Magnetic Susceptibility Signal Research Articles

Forcing factors of the magnetic susceptibility signal in lagoonal and subtidal depositional cycles from the Zachełmie section (Eifelian, Holy Cross Mountains, Poland)

Abstract Eifelian dolomites in the Zachełmie Quarry exhibit metre-scale depositional cyclicity, both in the lower, lagoonal part of the section and in the upper, shallow subtidal portion. Magnetic properties were studied in 30 samples (at c. 1 m intervals), including magnetic susceptibility (MS) and anhysteretic and isothermal remanent magnetization. The rock magnetic parameters are compared with the results of thin-section study and elemental chemistry. The forcing factors driving the MS pattern are identified. The MS signal is mostly related to a finely dispersed hematite, controlled by terrigenous input. Magnetite plays a subordinate role and it is confined to less terrigenous horizons relatively enriched in uranium and phosphorus. Results of high-resolution ( c. 8 cm intervals) MS field measurements show a good correlation with depositional shallowing-upwards cycles, especially in the lagoonal part of the section, where variations of rock magnetic properties and geochemical (redox and productivity) indices are very small. High MS values occur in the bottom part of the cycles and they decrease upwards. Time-series analyses of the MS signal reveal the dominance of c. 1.7 m cycles, grouped into c. 10 m bundles. The former cycles probably reflect precession-driven changes in monsoonal intensity, whereas the latter may have been controlled by 100 kyr eccentricity.

Magnetic susceptibility and geochemical characterization of an upper Mississippian cyclothemic section Polotnyanyi Zavod, (Moscow Basin, Russia)

Abstract This case study provides insight into magnetic susceptibility (MS), iron and bulk-sample geochemistry patterns in an Upper Mississippian siliciclastic–carbonate cyclothemic section Polotnyanyi Zavod (Moscow Basin, Russia), with many subaerial disconformities and Stigmaria impressions. The goal of this paper is to test whether the MS and geochemical signals in this section are linked to any specific geological processes. The section is dominated by limestones but contains several siliciclastic units and numerous subaerial disconformities. This lithological heterogeneity is vividly expressed on MS and bulk geochemical logs. MS shows the strongest positive correlation to bulk iron and also strong correlations to Al 2 O 3 , MgO, K 2 O and TiO 2 , pointing to close association of iron with siliciclastic fines rich in detrital mica and clays. The correlation of iron and MS to siliciclastic fines or subaerial exposure horizons is not straightforward. The highest ferruginization with most intense MS excursions occurs in basal sooty silts and shales of three main siliciclastic units of the studied section. In addition, many other thin pedogenized shales are ferruginized and show a relative high magnetism, but some ferruginized shales are not palaeosols.

One-dimensional lanthanide coordination polymers: synthesis, structures, and single-ion magnetic behaviour.

A family of isostructural one-dimensional (1D) lanthanide compounds with the formula [Ln(III)(L)(NO3)(DMF)2]∞, where Ln = Tb (1), Dy (2), Ho (3) and Er (4), was synthesised and structurally characterised. The magnetic behaviour of these compounds is demonstrated, and their static and dynamic properties are discussed and analyzed. The results of dc magnetic susceptibility measurements regarding compounds 1-4 indicate the existence of thermal depopulation of the crystal field-induced splitting of mJ levels of Ln ions, while the observed frequency-dependent out-of-phase ac magnetic susceptibility signals under certain magnetic fields for compounds 1, 2, and 4 show a slow relaxation of the magnetisation with an energy barrier of 6.15, 54.45, and 28.14 K, respectively. Also, complex 2 shows peak maxima of χM'' signals in temperature-dependent as well as frequency-dependent ac magnetic susceptibility measurements under an appropriate magnetic field, indicating that the relaxation process is dominantly thermally activated.

About this title ‐ Magnetic Susceptibility Application: A Window onto Ancient Environments and Climatic Variations

Magnetic susceptibility (MS) is a tool frequently used by geologists on sediments or rocks to perform correlations and sea-level or climatic reconstructions. Applied measurements are made on unoriented, bulk samples and bulk MS is mostly influenced by the magnetic mineral content of the rock and often interpreted as influenced by detrital inputs. Magnetic data acquisition is fast and straightforward and this allows the high-resolution sampling needed for palaeoclimatic research (e.g. spectral analysis). However, the link with detrital inputs is not always preserved and the impact of diagenesis on the final MS signal can blur primary information. This volume includes contributions dealing with the origin of the magnetic minerals, and the application of MS as a palaeoenvironmental or palaeoclimatic proxy and also as a tool to provide astronomical calibration in order to improve the chronology of selected time intervals.

The astronomical calibration of the Givetian (Middle Devonian) timescale (Dinant Synclinorium, Belgium)

Abstract Recent advances in radiometric dating result in significant improvements in the geological timescale and provide better insight into the timing of various processes and evolutions within the Earth's system. However, no radiometric ages are contained within the Givetian. Consequently, the absolute ages of the Givetian Stage boundaries, as well as the stage's duration, remain poorly constrained. As an alternative, the analysis of sedimentary cycles allows for the estimation of the duration of this stage. We examined the high-resolution magnetic susceptibility signals of four Givetian outcrops in the Givet area for a possible astronomical imprint, to fully understand the rates of evolutionary and environmental change. All four sections are firmly correlated and wavelet analyses of the magnetic susceptibility signals reveal the imprint of astronomical eccentricity forcing. The highly stable 405 kyr cycles constrain the duration of the Givetian Stage at 4.35±0.45 Myr, which is in good agreement with the International Chronostratigraphic Chart (5.0 Myr). The studied sections also exhibit an imprint of obliquity, suggesting a climatic teleconnection between low and high latitudes. The corresponding microfacies curves demonstrate similar astronomical imprint, and thereby indicate that the observed 10 5 year-scale cyclicity is the result of climatic and environmental change.

Geophysical signatures of disseminated iron minerals: A proxy for understanding subsurface biophysicochemical processes

Previous studies have linked biogeophysical signatures to the presence of iron minerals resulting from distinct biophysicochemical processes. Utilizing geophysical methods as a proxy of such biophysicochemical processes requires an understanding of the geophysical signature of the different iron minerals. Laboratory experiments were conducted to investigate the complex conductivity and magnetic susceptibility signatures of five iron minerals disseminated in saturated porous media under variable iron mineral content and grain size. Both pyrite and magnetite show high quadrature and inphase conductivities compared to hematite, goethite, and siderite, whereas magnetite was the highly magnetic mineral dominating the magnetic susceptibility measurements. The quadrature conductivity spectra of both pyrite and magnetite exhibit a well-defined characteristic relaxation peak below 10 kHz, not observed with the other iron minerals. The quadrature conductivity and magnetic susceptibility of individual and a mixture of iron minerals are dominated and linearly proportional to the mass fraction of the highly conductive (pyrite and magnetite) and magnetic (magnetite) iron minerals, respectively. The quadrature conductivity magnitude increased with decreasing grain size diameter of magnetite and pyrite with a progressive shift of the characteristic relaxation peak toward higher frequencies. The quadrature conductivity response of a mixture of different grain sizes of iron minerals is shown to be additive, whereas magnetic susceptibility measurements were insensitive to the variation in grain size diameters (1–0.075 mm). The integration of complex conductivity and magnetic susceptibility measurements can therefore provide a complimentary tool for the successful investigation of in situ biophysicochemical processes resulting in biotransformation or secondary iron mineral precipitation.

Tectonically controlled sedimentation: impact on sediment supply and basin evolution of the Kashafrud Formation (Middle Jurassic, Kopeh-Dagh Basin, northeast Iran)

The Kashafrud Formation was deposited in the extensional Kopeh-Dagh Basin during the Late Bajocian to Bathonian (Middle Jurassic) and is potentially the most important siliciclastic unit from NE Iran for petroleum geology. This extensional setting allowed the accumulation of about 1,700 m of siliciclastic sediments during a limited period of time (Upper Bajocian–Bathonian). Here, we present a detailed facies analysis combined with magnetic susceptibility (MS) results focusing on the exceptional record of the Pol-e-Gazi section in the southeastern part of the basin. MS is classically interpreted as related to the amount of detrital input. The amount of these detrital inputs and then the MS being classically influenced by sea-level changes, climate changes and tectonic activity. Facies analysis reveals that the studied rocks were deposited in shallow marine, slope to pro-delta settings. A major transgressive–regressive cycle is recorded in this formation, including fluvial-dominated delta to turbiditic pro-delta settings (transgressive phase), followed by siliciclastic to mixed siliciclastic and carbonate shoreface rocks (regressive phase). During the transgressive phase, hyperpycnal currents were feeding the basin. These hyperpycnal currents are interpreted as related to important tectonic variations, in relation to significant uplift of the hinterland during opening of the basin. This tectonic activity was responsible for stronger erosion, providing a higher amount of siliciclastic input into the basin, leading to a high MS signal. During the regressive phase, the tectonic activity strongly decreased. Furthermore, the depositional setting changed to a wave- to tide-dominated, mixed carbonate–siliciclastic setting. Because of the absence of strong tectonic variations, bulk MS was controlled by other factors such as sea-level and climatic changes. Fluctuations in carbonate production, possibly related to sea-level variations, influenced the MS of the siliciclastic/carbonate cycles. Carbonate intervals are characterized by a strong decrease of MS values indicates a gradual reduction of detrital influx. Therefore, the intensity of tectonic movement is thought to be the dominant factor in controlling sediment supply, changes in accommodation space and modes of deposition throughout the Middle Jurassic sedimentary succession in the Pol-e-Gazi section and possibly in the Kopeh-Dagh Basin in general.

Application of magnetic susceptibility as a paleoclimatic proxy on Paleozoic sedimentary rocks and characterization of the magnetic signal – IGCP-580 projects and events

The International Geoscience Program project IGCP-580 (started in 2009), focuses on the application of magnetic susceptibility (MS) as a paleoclimatic proxy on Paleozoic sedimentary rocks and on the characterization of the magnetic susceptibility signal. Here we provide a summary of the scientific targets behind the project and a summary of the organized activities. This project concerns three main issues: the first one consists of compiling the available MS data from the different researchers and continuing the collection of new data (with a main focus on the Devonian). The second issue focuses on the identification of the nature and origin of the magnetic minerals carrying MS signal. The last issue concerns the application of MS as a correlation, cyclostratigraphic and paleoclimatic tool. The IGCP-580 community consists of 245 researchers, from 45 countries (including Kenya, Namibia, Vietnam, Iran, Uzbekistan, Algeria, Tunisia, Colombia, Nigeria, India, etc.). During the project, we organized five meetings (Belgium, China, Czech Republic, Austria, Canada), three special sessions in international meetings and eight field workshops, as well as various training sessions.

Low-latitude climate variability in the Heinrich frequency band of the Late Cretaceous greenhouse world

Abstract. Deep marine successions of early Campanian age from DSDP (Deep Sea Drilling Project) site 516F drilled at low paleolatitudes in the South Atlantic reveal distinct sub-Milankovitch variability in addition to precession, obliquity and eccentricity-related variations. Elemental abundance ratios point to a similar climatic origin for these variations and exclude a quadripartite structure as an explanation for the inferred semi-precession cyclicity in the magnetic susceptibility (MS) signal as observed in the Mediterranean Neogene for precession-related cycles. However, semi-precession cycles as suggested by previous work are likely an artifact reflecting the first harmonic of the precession signal. The sub-Milankovitch variability, especially in MS, is best approximated by a ~7 kyr cycle as shown by spectral analysis and bandpass filtering. The presence of sub-Milankovitch cycles with a period similar to that of Heinrich events of the last glacial cycle is consistent with linking the latter to low-latitude climate change caused by a non-linear response to precession-induced variations in insolation between the tropics.

Magma flow directions in the sheeted dike complex at superfast spreading mid-ocean ridges: Insights from IODP Hole 1256D, Eastern Pacific

Integrated Ocean Drilling Program (IODP) Hole 1256D successfully sampled a complete section of an intact oceanic crustal sheeted dike complex (SDC) (from 1061 to 1320 meters below seafloor; mbsf) on a 15 Ma old Cocos Plate. A series of rock magnetic measurements were carried out to understand the magmatic processes that accreted this end-member, superfast-spread (200 mm/yr full rate) oceanic crust. Results indicate that main ferromagnetic minerals are predominantly pseudo single-domain (titano)magnetite crystals, responsible for both anisotropy of magnetic susceptibility (AMS) and magnetic remanence signals. AMS fabrics were reoriented into a geographic reference frame using magnetic remanence data, and corrected for a counterclockwise rotation of the Cocos Plate relative to the East Pacific Rise (EPR) ca. 15 Ma. Corrected AMS fabrics were then compared with the orientations of chilled margins previously obtained from Formation MicroScanner (FMS) images of the SDC at Hole 1256D. For some samples taken from close to dike margins, a dike-normal orientation of the minimum AMS axes (Kmin) of prolate AMS ellipsoids mean that the long axis (Kmax) can be used to infer magma flow directions. Subvertical Kmin orientations in the interior of the dikes, however, may have required settling or compaction of the magma shortly after intrusion, thus rearranging the AMS fabric. Despite this orientation of Kmin axes, orientation of Kmax axes indicate a rather constant subhorizontal paleo-flow direction, suggesting that magmas most probably traveled to the surface considerable distances from source regions within the EPR system.

Contribution of the Magnetic Susceptibility to the Characterization of the Babouri-Figuil Cretaceous Basin

Magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion. This work, aims to show that, the magnetic susceptibility signature which exists in the cretaceous sediments of the Babouri-Figuil basin, resides mainly in the detrital constituents. Variations of amplitudes are observed, which can be useful for regional correlation.This amplitude variation results in the transgressive and regressive movements that give way to a fluctuation of detrital deposits because of erosion. Considering the sedimentological study, carried out, different microfacies have been identified in the basin, namely, fluvial facies and lake facies that sometimes contain fossils. The combination of detailed sedimentological analysis and sequence stratigraphy is based on the modeling of vertical and lateral variations within the basin. Finally, the interpretation of the magnetic susceptibility signal suggests that in the detrital domain, this signal is mainly controlled by environmental parameters such as the agitation of the water and the rate of sedimentation, as well as diagenesis.

A rock magnetic study on red palaeosols in Yun-Gui Plateau (Southwestern China) and evidence for uplift of Plateau

Magnetic signals of red palaeosols from the Yun-Gui Plateau (YGP), southwestern China, are studied using rock magnetism, selective chemical dissolution, differential X-ray diffraction (DXRD) and high-resolution transmission electron microscopy (HRTEM) in order to explore the potential of red palaeosol as a proxy indicator of paleogenesis and uplift of plateau. Red palaesols are characterized by highly magnetic signals and dark red color with a hue of 5 YR (yellow-red). The low-frequency magnetic susceptibility (χlf) of topsoils is shown to vary from 1500 × 10−8 to 2500 × 10−8m3 kg−1 in a decreasing pattern from the top to bottom of the profile. Magnetic profiles reveal that the red palaeosols contain significant amount of fine-grained superparamagnetic (SP) grains, which is attributed to the higher concentration of pedogenic SP maghemite. The dithionite–citrate–bicarbonate (DCB) procedure can selectively dissolve ultrafine pedogenic magnetic minerals in the red palaeosols, as evidenced by the highly correlation between mass-specific frequency-dependent magnetic susceptibility (χfd) and χlf loss of DCB treatment. The magnetic loss after DCB treatment accounts for 87–95 per cent of the original susceptibility. Rock magnetism and DXRD reveal that the main magnetic mineral in the red palaeosols is the pedogenic SP/stable single domain (SP/SSD) maghemite. These pedogenic maghemites account for about 1 per cent of free iron oxides. HRTEM observations show the evidence of pedogenic SP (<∼20–30 nm) and pure maghemite. These magnetic particles vary from several to tens of nanometres in size and exhibit typical crystallochemical characteristics of this mineral. Magnetic evidence suggests that the red palaeosols experience a strongly pedogenic processes. Pedogenic processes result in the neoformation of hematite and maghemite, and causes a substantial increase in the magnetic susceptibility and other magnetic signals. Therefore, the rock magnetism of red palaeosols potentially yields significant palaeopedogenic information and evidence on the neotectonic movement of plateau. Results of the present work suggest that the red palaeosols could be a good tool for understanding the amplitude and the age of uplift in the YGP.

Pedogenic modification of magnetic susceptibility signals recording paleoclimate – an explanation of regional changes to Alaskan, Chinese and Siberian loess

Pedogenic modification of magnetic susceptibility signals recording paleoclimate – an explanation of regional changes to Alaskan, Chinese and Siberian loess

Magnetic susceptibility and its relationship with paleoenvironments, diagenesis and remagnetization: examples from the Devonian carbonates of Belgium

To better understand the origin of the initial magnetic susceptibility (χin) signal in carbonate sequences, a rock magnetic investigation that includes analysis of acquisition curves of the isothermal remanent magnetization (IRM) and hysteresis parameters, was undertaken on Devonian carbonates from the Villers and Tailfer sections, Belgium. Both sections are divided into a lower unit, dominated by biostromal and external ramp facies (biostromal unit) and an upper unit, only consisting of lagoonal facies (lagoonal unit). The variations in χin signal are mainly driven by magnetite variation, mostly pseudo-single-domain (PSD) magnetite. Clay minerals, pyrite, hematite and obviously calcite and dolomite are also present but their contribution to the χin pattern is not significant. There is a correlation between detrital proxies (Zr, Rb, Al2O3, TiO2) and χin for the Tailfer biostromal unit and the entire Villers section. The pervasive presence of fine-grained magnetite is interpreted as related to remagnetization. In absence of external fluids, the iron released during the smectite to illite transition remains in situ. In those situations χin may reflect an inherited primary synsedimentary signal. In the lagoonal unit of the Tailfer section, remagnetization appears to have obscured the original detrital information prompting the need for an evaluation of the composition of the susceptibility signal for individual case studies.

An orbital floating time scale of the Hauterivian/Barremian GSSP from a magnetic susceptibility signal (Río Argos, Spain)

An orbital floating time scale of the Hauterivian–Barremian transition (Early Cretaceous) is proposed using high-resolution magnetic susceptibility measurements. Orbital tuning was performed on the Río Argos section (southeast Spain), the candidate for a Global boundary Stratotype Section and Point (GSSP) for the Hauterivian–Barremian transition. Spectral analyses of MS variations, coupled with the frequency ratio method, allow the recognition of precession, obliquity and eccentricity frequency bands. Orbitally-tuned magnetic susceptibility provides minimum durations for ammonite biozones. The durations of well-constrained ammonite zones are assessed at 0.78myr for Pseudothurmannia ohmi (Late Hauterivian) and 0.57myr for Taveraidiscus hugii (Early Barremian). These results are consistent with previous estimates from the other reference section (Angles, southeast France) and tend to show that the Río Argos section displays a complete succession for this time interval. They differ significantly from those proposed in the Geologic Time Scale 2008 and may help to improve the next compilation. The Faraoni Oceanic Anoxic Event, a key Early Cretaceous oceanographic perturbation occurring at the P. ohmi/P. catulloi subzone boundary has a duration estimated at 0.10–0.15myr, which is similar to previous assessments.

Single Molecule Magnet Behavior of a Pentanuclear Mn-Based Metallacrown Complex: Solid State and Solution Magnetic Studies

The magnetic behavior of the pentanuclear complex of formula Mn(II)(O(2)CCH(3))(2)[12-MC(Mn(III)(N)shi)-4](DMF)(6), 1, was investigated using magnetization and magnetic susceptibility measurements both in the solid state and in solution. Complex 1 has a nearly planar structure, made of a central Mn(II) ion surrounded by four peripheral Mn(III) ions. Solid state variable-field dc magnetic susceptibility experiments demonstrate that 1 possesses a low value for the total spin in the ground state; fitting appropriate expressions to the data results in antiferromangetic coupling both between the peripheral Mn(III) ions (J = -6.3 cm(-1)) and between the central Mn(II) ion and the Mn(III) ones (J' = -4.2 cm(-1)). In order to obtain a reasonable fit, a relatively large single ion magnetic anisotropy (D) value of 1 cm(-1) was necessary for the central Mn(II) ion. The single crystal magnetization measurements using a microsquid array display a very slight opening of the hysteresis loop but only at a very low temperature (0.04 K), which is in line with the ac susceptibility data where a slow relaxation of the magnetization occurs just around 2 K. In frozen solution, complex 1 displays a frequency dependent ac magnetic susceptibility signal with an energy barrier to magnetization reorientation (E) and relaxation time at an infinite temperature (τ(o)) of 14.7 cm(-1) and 1.4 × 10(-7) s, respectively, demonstrating the single molecule magnetic behavior in solution.

Non-magnetic indicators of pedogenesis related to loess magnetic enhancement and depletion: Examples from the Czech Republic and southern Siberia

We carried out a multiparameter investigation for non-magnetic proxies of the intensity of pedogenesis in loess/paleosol sections from two different climate settings, Dolní Věstonice, central Europe, and Krasnogorskoye, southern Siberia. The work was performed in order to clarify the problem of two opposite scenarios of magnetic susceptibility (MS) patterns in these two profiles, the “Chinese” model with magnetically enhanced paleosols and the “Siberian/Alaskan” model with magnetically depleted paleosols. The age constraints on the Krasnogorskoye section were inferred from an independent correlation with the well-dated Dolní Věstonice section, based on MS and sediment color (CIE L ∗ ), and with the MS log from Lake Baikal. The pedologic description of the loess/paleosol sections and their correlation was considerably improved by the use of Vis spectral proxies (CIE L ∗ , reflectance in the red band); their weathering intensity can be effectively characterized by diffuse reflectance spectroscopy (DRS) and geochemical (CEC and Rb/Sr) proxies. Whereas the MS is strongly dependent on the type of soil (chernozems vs. brown soils), the geochemical proxies, in particular CEC, proved to be relatively independent of the soil type. These parameters are less affected by region-specific conditions than the MS signal. The non-magnetic proxies indicate relatively dissimilar climatic trends at the two sites during the last glacial–interglacial cycle. A long-distance correlation, based solely on the MS signal, can be adversely affected by switching between the Chinese and the Siberian/Alaskan magnetic modes, this having been observed at the Krasnogorskoye section. In general, no single universal proxy of weathering or pedogenesis intensity would be applicable across broad regions or considerable climatic gradients. Paleoclimatologic interpretations of large regions should always be based on a carefully designed, multi-proxy approach.

Mixed-metal single-molecule magnets: Syntheses, structure, and magnetic properties of [Mn 8Fe 4O 12(O 2CR) 16(H 2O) 4] (R = CH 2Cl, CH 2Br, CHCl 2)

Three mixed-metal single-molecule magnets containing [Mn 8Fe 4O 12] 16+ cores are synthesized and characterized. The reaction of FeCl 2·4H 2O with KMnO 4 and RCOOH (R = CH 2Cl, CH 2Br) in H 2O gives [Mn 8Fe 4O 12(O 2CR) 16(H 2O) 4] (R = CH 2Cl ( 1), CH 2Br ( 2)) in yields of 43% and 40%, respectively. Treatment of complex 1 with an excess of CHCl 2COOH in CH 2Cl 2 gives [Mn 8Fe 4O 12(O 2CCHCl 2) 16(H 2O) 4]·CH 2Cl 2·10H 2O ( 3·CH 2Cl 2·10H 2O) in a yield of 83%. The X-ray structure analysis reveals that all three complexes consist of a trapped-valence dodecanuclear core comprising 4Mn III, 4Fe III, and 4Mn IV ions. DC magnetic susceptibility and magnetization measurements indicate that all three complexes exhibit intramolecular antiferromagnetic interaction, resulting in an S = 4 ground state. In addition, frequency-dependent out-of-phase AC magnetic susceptibility signals at low temperature for complexes 1, 2, and 3 are indicative of their single-molecule magnetism behavior.

Pragian–Emsian successions in Uzbekistan and Bohemia: magnetic susceptibility logs and their dynamic time warping alignment

High-resolution low-field magnetic susceptibility (MS) logs of the Lower Devonian limestone beds of the Zeravshan–Gissar Mountain Region (Uzbekistan in Central Asia) and Prague Synform (Barrandian area, Bohemia, Czech Republic, Europe) were stratigraphically correlated using dynamic timewarping (DTW) alignment techniques that are sensitive to local variations in sediment accumulation rates. A method of adjustment of raw data before the actual DTW alignment was developed in order to eliminate multiple sources on the MS signal, and a successful MS-DTW correlation was performed between the Zinzilban Gorge section in Uzbekistan and the Pozar-3 section in Bohemia. The results basically corroborate some of the most recent biostratigraphic correlations, especially those suggested by P. Carls and J.I. Valenzuela-Rios, and provide a 10- to 100-fold better resolution. The projection of the basal Emsian Global Boundary Stratigraphic Section and Point (GSSP) in the Zinzilban Gorge (Uzbekistan) to the succession of Bohemian strata points to a level in the lower parts of the Lodenice Limestone, i.e., to the lowermost one-third of the Praha Formation. Hence, more than two-thirds of the original Pragian in Bohemia (~Praha Formation) remain above the basal Emsian GSSP level in Uzbekistan. This implies that the decision about this GSSP ratified by IUGSin August 1996 led to a significant reduction of the extent of the original Pragian to only its oldest strata. Many other stratigraphically correlatable levels were identified within the sequences of MS stratigraphic patterns in these two widely separated sections in spite of the fact that the Pragian–Emsian palaeoclimatic conditions of the northern hemisphere were different from those of the southern hemisphere. The base of the Norbonak Beds at Zinzilban corresponds to a stratigraphic level lying ~3.6m below the base of the Zlichov Limestone in the Pozar-3 section. The Bohemian anoxic Graptolite Event correlates to a level about 3m below the boundary of the Zinzilban and Norbonak beds at Zinzilban.

Bead magnetorelaxometry with an on-chip magnetoresistive sensor

Magnetorelaxometry measurements on suspensions of magnetic beads are demonstrated using a planar Hall effect sensor chip embedded in a microfluidic system. The alternating magnetic field used for magnetizing the beads is provided by the sensor bias current and the complex magnetic susceptibility spectra are recorded as the 2nd harmonic of the sensor response. The complex magnetic susceptibility signal appears when a magnetic bead suspension is injected, it scales with the bead concentration, and it follows the Cole-Cole expression for Brownian relaxation. The complex magnetic susceptibility signal resembles that from conventional magnetorelaxometry done on the same samples apart from an offset in Brownian relaxation frequency. The time dependence of the signal can be rationalized as originating from sedimented beads.