Rapid Magnetic Susceptibility Characterization of Coastal Morphosedimentary Units at Two Insular Strandplains in Estonia (original) (raw)
Related papers
Baltica, 2023
A diverse suite of erosional features along the shoreline of Lehtma (Hiiumaa Island, Estonia) is used to assess their morphodynamic context and preservation potential. The Holocene strandplain along the eastfacing (leeward) shoreline has experienced rapid retreat due to the anthropogenically induced sediment deficit. The study site is located just updrift of the erosional-depositional fulcrum segment, with southerly longshore transport resulting in the accumulation of eroded sand along a drift-aligned spit. The most prominent erosional indicators are mature pine trees in different stages of undercutting, toppling, fragmentation, and burial. Morphological features include scarps in paleo-beach/dune ridges (height: > 1 m), as well as modern berm scarps. Mineralogical indicators are exemplified by heavy-mineral concentrations (HMCs) of variable thickness (some > 2 cm) and concentration. Representative samples show a substantial increase in bulk low-field magnetic susceptibility ranging from < 10 µSI common to the nearby Holocene coastal lithosomes to > 8,000 µSI in secondcycle HMCs within berm enrichment zones. A conceptual morphosedimentary model describing the recent and current state of the system, as well as the preservation potential of specific structures and recognition in geological research (e.g., georadar signatures of buried trees and HMCs) is proposed. The approach presented in this study can be used to assess the distribution and preservation potential of erosional indicators along the Baltic Sea coast and mineralogically heterogeneous, forested sandy shorelines worldwide.
Magnetic susceptibility of Middle Ordovician sedimentary rocks, Pakri Peninsula, NW Estonia
Estonian Journal of Earth Sciences, 2016
Magnetic susceptibility (MS), its frequency-dependence and anisotropy of the Middle Ordovician Dapingian and Darriwilian sedimentary sequence from three sites (Uuga, Testepere and Leetse) in the Pakri Peninsula, NW Estonia are analysed in combination with the mineralogical composition. The study is based on 463 cores drilled at intervals of a few centimetres to a maximum of about 1 m. All the samples show low and positive MS, which suggests the presence of small quantities of paraand/or ferromagnetic minerals. The stratigraphic units of the three studied sites have a similar along-section appearance, which provides a base for a composite curve. The relatively higher susceptibilities are carried by secondary Fe-Ti oxides (Toila Formation), goethite ooids (Kandle Formation) and ferrous dolomite (Pae Member), whereas paramagnetic minerals are mostly responsible for the rest of the sequence. Considering the dependence of MS on regressive-transgressive cycles (high/low MS within deposits of regressive/transgressive parts of the cycles, respectively), the MS data do not agree with sedimentologically derived sea-level compilations. The measured changes in MS in the Pakri Peninsula outcrops correlate at certain characteristic levels with those deposited in the deeper part of the palaeobasin (Viki core), indicating that the post-depositional iron mobilization within the sediments took place at least at a regional level. Because of post-depositional reorganization of ferromagnetic carrier minerals, the MS values may, however, not be used as a detrital proxy.
Magnetic susceptibility of Late Weichselian deposits in southeastern Sweden
Boreas, 2008
The magnetic susceptibility of Late Weichselian glacial, late-glacial and post-glacial deposits from Blekinge. southeast Sweden. has been measured. The susceptibility variations proved to be dependent upon the particle size distribution of the sample and the type of bedrock from which the deposit is derived. Comparison of susceptibility variations in the Baltic Ice Lake and lacustrine sediments with biologicdl indicators of environmental change suggests that susceptibility can be a useful complement to studies aimed at identifying lake isolation, climatic change or changes in erosion within the catchment. The results also suggest that comparison of susceptibility versus fraction size curves can aid lithostrdtigraphic division of unconsolidated deposits.
Magnetic history of Early and Middle Ordovician sedimentary sequence, northern Estonia
Geophysical Journal International, 2010
Alternating field and thermal demagnetization of lime-and dolostones from the Lower and Middle Ordovician (Floian to Darriwilian stages) subhorizontally bedded sequences in NW and NE Estonia reveal two characteristic magnetization components (named P and S). The intermediate-coercivity (demagnetized at 30-60 mT, up to 300-350 • C) reversed polarity component P (mean of Floian Stage: D ref = 147.8 ± 10.8 • , I ref = 65.8 ± 5.4 • ; combined mean of Dapingian and Darriwilian stages: D ref = 166.0 ± 8.4 • , I ref = 56.1 ± 6.5 • ) is regarded as the primary remanence of early diagenetic (chemical) origin. On the Baltica's apparent polar wander path (APWP), the palaeopoles (Floian: Plat = 25.0 • N, Plon = 50.8 • E, K = 52.7, A 95 = 7.2 • ; Dapingian and Darriwilian: Plat = 11.4 • N, Plon = 39.1 • E, K = 33.8, A 95 = 6.7 • ) are placed on the Lower and Middle Ordovician segment.
Palaeomagnetism and magnetomineralogy of a Holocene lake sediment from Vågsøy, western Norway
Physics of the Earth and Planetary Interiors, 1981
Stable remanent directions encountered in three oriented lake-sediment cores, covering 6 m of gyttja deposits, reveal declination swings with amplitudes of the order of ± 500. Anomalously low inclinations, scattered around the horizontal in the upper 2 m of core, is attributed to compressional disturbances of the alignment of magnetic grains during the coring procedure. Four~dates obtained (1250, 1940, 4600 and 6330 y B.P.) have enabled a correlation with features 'c'-'g' of the British Geomagnetic Master Curve). For the older part of the curve, features 'h' and 'i', the correlation is questionable. Magneto-mineralogical parameters and qualitative chemical analysis of individual grains by secondary X-ray emission analysis reveal the presence of pure magnetite grains. Scanning electron micrographs show a dominant proportion of concoidal slightly elongated grains (10-80 s m). A few almost-perfect octahedral magnetite crystals can be related to outcrops of augen gneisses in the vicinity confirming a detrital origin of these grains.
Global and Planetary Change, 2018
Paleomagnetic and rock magnetic data were measured on glaciomarine silty-clay successions along an E-W sediment-core transect across the continental shelf and slope of the Kveithola paleo-ice stream system (south of Svalbard, northwestern Barents Sea), representing a stratigraphic interval spanning the last deglaciation and the Holocene. The records indicate that magnetite is the main magnetic mineral and that magnetic minerals are distinctly less abundant on the shelf than at the continental slope. The paleomagnetic properties allow for the reconstruction of a well-defined characteristic remanent magnetization (ChRM) throughout the sedimentary successions. The stratigraphic trends of rock magnetic and paleomagnetic parameters are used for a shelf-slope core correlation and sediment facies analysis is applied for depositional processes reconstruction. The new paleomagnetic records compare to the PSV and RPI variation predicted for the core sites by a simulation using the global geomagnetic field variation models SHA.DIF.14k and CALS7K.2 and closest PSV and RPI regional stack curves. The elaborated dataset, corroborated by available 14 C ages, provides a fundamental chronological framework to constrain the coupling of shelf-slope sedimentary processes and environmental changes in the NW Barents Sea region during and after deglaciation.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2008
It has been clearly demonstrated that past climate fluctuations are recorded in marine sedimentary rocks. However, for many reasons, extracting the climate signature is difficult. Initial low-field mass-specific magnetic susceptibility (MS) data can potentially provide a measure of climate variability and thus become a proxy characterizing climate cyclicity in a wide range of marine sediments. This is due to the fact that climate change (warm, wet versus cold, dry) drives cyclic weathering and erosional variations that are recorded as the detrital components of marine sediment that dominates the MS. To test the utility of MS to yield climate proxies in marine sediments showing major changes in lithology, we have sampled the well-studied Danian/Selandian boundary interval (Lower Paleocene) at Zumaia (Zumaya), Spain. This interval represents a dramatic, rapid lithologic change from Danian carbonate-dominated limestone-marl couplets to a detrital-dominated marl-shale sequence in the Selandian, indicating onset of a major regression-erosional event beginning in the lowest Selandian. Sampling included a continuous sequence from the uppermost Danian Stage (3.71 m) into the lowermost Selandian Stage (5.2 m), a suite of 175 samples collected at 5 cm intervals. Our results indicate that MS measurements reflect changes in detrital sediment at the site, first by closely tracking high-frequency limestone-marl couplets, second with a large, rapid shift toward higher MS values beginning at the Danian/Selandian boundary resulting from a major regression, and third by tracking low-frequency climate-controlled variations known to have occurred during deposition of these sediments. MS zones developed from the cyclicity observed throughout the sequence, supported by time series analysis using Fourier Transform (FT) methods applied to the MS results, exhibit Milankovitch cyclicities in the precessional (19-24 kyr), obliquity (41-54 kyr) and eccentricity bands (100 kyr). This is in excellent agreement with previous FT work on the section using measured variations in cyclic bed thicknesses. With the new MS data set and FT results, we then developed a Floating Point Time Scale (FPTS) for the sequence sampled (covering ∼ 550 kyr through the Danian/Selandian boundary interval), yielding a time-scale resolution for the uppermost Danian to ∼ 10,000 years. However, only the ∼ 100,000 year eccentricity band for the Selandian is sufficiently well developed for an FPTS estimate, and yields a time-scale resolution of ∼ 50,000 years. Our test of the utility of MS data sets in this varying depositional setting demonstrated that these data can provide a climate proxy that is not disrupted by large lithologic changes.