1,720,976 research outputs found
Grain-size distribution and grain-size dependent magnetic susceptibility of sediment core GeoB18530-1
No full textSince the weight percentages of (classifiable) IRD particles > 1 mm and (unclassifiable, but separable) IRD particles > 125 µm both largely underestimate the total content and magnetic impact of IRD, it is important to quantify also the finer IRD fractions and their magnetic susceptibilities. From each of the IRD-rich sediment units H1, I1 and H2, six magnetic cube samples of 6.2 cm³ each were combined, dried, weighed and ultrasonically suspended in water. These three slurries were successively washed through 16 stacked sieves with mesh sizes in approximately 0.5 phi steps from 4000 µm to 5 µm using a Fritsch wet sieve shaker. The sieve fractions were carefully collected, dried, weighed and measured in a Kappabridge KLY2 susceptometer. The data and therefrom-derived partial susceptibilities and cumulative distributions clearly demonstrate that the magnetically most dominant and "volatile" sediment particles fall into the 40-125 µm range. Detrital particles of such sizes are too coarse to have been current-transported over long distances and were therefore probably at least partially ice-rafted
Rock magnetic, geochemical and sedimentological properties related to IRD composition and content of sediment core GeoB18530-1
No full textThe IRD-rich Heinrich Event (HE) layers of gravity core GeoB18530-1, retrieved from the SE Grand Banks slope of Newfoundland, coincide with bulk magnetic susceptibility maxima. This positive correlation of IRD content and susceptibility is widely observed and at first glance contradictive, since detrital dolomite, the most common IRD component, is weakly magnetic and should therefore reduce rather than enhance bulk magnetic susceptibility. As Part I of the associated manuscripts (Bukar et al., 2025a, doi:10.1029/2024GC011930) showed, the petrology of HLs is rather diverse; some prominent magmatic and metamorphic IRD species should actually have relatively high magnetic susceptibilities. This data set bundle comprises a collection of bulk rock magnetic, geochemical and sedimentological sediment records revealing the influence of specific magnetic mineral fractions, IRD lithologies and textural properties on the magnetic susceptibility signal. Part II of the associated manuscripts (Bukar et al., 2025b, doi:10.1029/2024GC011931) also features so far unreported rock magnetic property data of all observed IRD lithologies. These susceptibility, IRM, ARM and HIRM data were acquired from large or pooled (granule to gravel size) classified IRD specimens. Since IRD particles are not limited to larger grain sizes, three composite bulk sediment samples from units H1, I1 and H2 were wet-sieved to reveal the grain-size dependence of magnetic susceptibility. Six linear regression models finally compare the predictability of magnetic susceptibility from rock magnetic, geochemical, sedimentological and petrological data
Principal Component Analysis (PCA) of IRD content in Heinrich Event layers (H1-H5a) and interlayers (I1-I5) of sediment core GeoB18530-1
No full textThe data matrix of 192 classified IRD count data from H1-H5a and I1-I5 (excluding I6 because of too low IRD counts) by 22 IRD lithologies (https://doi.pangaea.de/10.1594/PANGAEA.971280) was row-normalized to 100% to give equal weight to all IRD assemblages independently of their specific IRD abundance, but not column-normalized in order to limit the influence of rare, statistically less relevant IRD lithologies. A Principal Component Analysis (PCA) of this data set reveales well interpretable PCA scores and disparate loadings for the first 5 PCA axes. PC1 reflects the contribution of Ooid-bearing Dolomite IRD, PC2 discriminates Muscovite-Biotite Granite IRD from other silicious IRD species, PC3 delineates Shale IRD vs. Hematite-stained Quartz IRD variability, PC4 quantifies Sucrosic Dolomite IRD and PC5 Microcline IRD percentage. We provide Heinrich layer and interlayer affiliations of all PCA scores, which some PC axes separate well, in particular PC1
Six linear regression models for the magnetic susceptibility of sediment core GeoB18530-1
No full textSix linear regression estimates of magnetic susceptibility were empirically tested for their ability to predict distinct HLs and ILs signal patterns. As predictors, we used MD magnetite content (IRM 20 mT), magnetic grain size (SIRM/X), dolomite and granite proxies (Ca/Sr and K/Fe), bulk porosity (%), dolomite and granite counts, and counts of the major 13 IRD species. As the obtained numbers and residues demonstrate, the rock magnetic proxies yield the best fits, followed by element ratios and porosity. The count-based predictors are incapable of estimating the older HLs 3-H5a and ILs 4-6 correctly; their regression coefficients also do not conform to the measured susceptibilities of the IRD species
Rock magnetic properties of petrologically representative IRD particles in sediment core GeoB18530-1
No full textIn order to determine the bulk magnetic impact of all 22 classified IRD lithologies, the specific petromagnetic properties of each were investigated in detail. In order to represent host rock composition as good as possible and to meet the magnetometric sensitivity requirements, the largest available IRD particles (dropstones) of each IRD species were selected, that were typically of granule or pebble size. Where such large particles were not available, several petrologically similar coarse sand-sized particles were combined in one sample. Great care was taken in sample preparation and sample holder correction to reach reliable values even for small and low-magnetic samples. In addition to magnetic properties, we also provide averaged IRD counts of HLs and in ILs for each IRD lithology
Isothermal Remanent Magnetization (IRM) acquisition curves for petrologically representative IRD particles of sediment core GeoB18530-1
No full textIRM acquisition curves (and their derivatives) resolve the cumulative coercivity distribution (and spectrum) of a magnetic mineral assemblage. Here we present data of larger, petrologically representative IRD particles of all observed lithologies. These IRM acquisition curves were acquired in logarithmically increasing pulse field steps from 10 mT to 2600 mT and measured by DC SQUIDS inside the 2G rock magnetometer without exposure to the external geomagnetic field. The varying magnetic peak field values shown here are based on real time peak field measurements by an integrated induction coil. Although samples were previously AF demagnetized, some samples have hard initial remanent magnetizations that were not entirely removed
Unclassified IRD susceptibility and content, porosity and grain density of sediment core GeoB18530-1
No full textIRD content is commonly assessed by weighing the detrital particles of the >125µm or > 1mm sieve fractions or by counting the IRD particles of the latter. Here we present these three sedimentological records together with the correctly measured, but numerically rather erratic magnetic susceptibility record of the IRD > 1mm fraction. The spiky character of sieved IRD susceptibility displays the stochastic nature of large IRD particle deposition. Systematic variations in IRD coarseness (calculated as ratio of IRD > 1mm and IRD >125µm) and bulk sediment porosity suggest considerable grain size variability of the glaciomarine Sediment fraction, while bulk particle density is almost constant at values of 2.7-2.8 g/cm³
Isothermal Remanent Magnetization (IRM) acquisition curves for the unclassified IRD > 1mm fractions of sediment core GeoB18530-1
No full textIRM acquisition curves (and their derivatives) resolve the cumulative coercivity distribution (and spectrum) of a magnetic mineral assemblage. Here we present IRM data for all extracted unclassified IRD > 1mm fractions. The IRM acquisition curves were acquired in logarithmically increasing pulse field steps from 10 mT to 2600 mT and measured by DC SQUIDS inside the 2G rock magnetometer without exposure to the external geomagnetic field. The varying magnetic peak field values shown here are based on real time peak field measurements by an integrated induction coil. Although samples were previously AF demagnetized, but some samples have hard initial remanent magnetizations, that could not be entirely removed
Nonlinear Mapping (NLM) analysis of IRD content in Heinrich Event layers (H1-H5a) and interlayers (I1-I5) of sediment core GeoB18530-1
No full textThis 3D data set represents the result of a Sammon projection (Sammon, 1969; https://doi.org/10.1109/T-C.1969.222678), where the mean relative proportions of all classified IRD lithologies for layers H1-H5a and IL1-IL5 were scaled down from the 22-dimensional parameter space into a presentable 3D space with the least possible change of point-to-point distance by Non-Linear Mapping (NLM). The spatial configuration depicted in Figure 9d of the associated publication (Bukar et al., 2024) visualizes the overriding compositional distinctiveness of Heinrich layers from Interlayers, but also the variability within each of these periods; in particular layers H3 and H6 as well as Last Glacial maximum interlayer I1 differ considerably from comparable situations
IRD composition and accumulation rates of Heinrich Event layers (H1-H5a) and interlayers (I1-I5) in sediment core GeoB18530-1
No full textThe cumulative classified count record (in percentages) over ~2 cm resolution of each petrologically identified IRD lithologies within the stratigraphic units of Heinrich Layers and Interlayers (about ~10 to 20 samples of 10 cm3) represent the >1 mm IRD particles in ~100 to 200 cm3 of sediments. The data are expressed in percentage to facilitate correlation and also avoiding exaggeration of less signification IRD particle abundances. IRD accumulation rate per area and time was derived from IRD counts and sedimentation rate of each stratigraphic unit
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