Characterization of individual rock magnetic components by analysis of remanence curves. 3. Bacterial magnetite and natural processes in lakes

Egli, Ramón

doi:10.1016/j.pce.2004.03.010

Cited by 140 publications

(166 citation statements)

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“…These bacteria produce magnetite (Blakemore, 1975;Frankel et al, 1979) or greigite (Heywood et al, 1990;Mann et al, 1990) crystals, so-called magnetosomes, within or outside their cells. It was shown that production of bacterial magnetite is linked to increasing organic matter supply (Egli, 2004a;Roberts et al, 2011b;Snowball et al, 2002), at least for oxic lakes (Egli, 2004b). Moreover, the production of bacterial magnetite can be fostered by the input of nutri-ents (Egli, 2004b).…”

Section: Bacterial Magnetite In Lake Ohrid Sediments?mentioning

confidence: 99%

“…It was shown that production of bacterial magnetite is linked to increasing organic matter supply (Egli, 2004a;Roberts et al, 2011b;Snowball et al, 2002), at least for oxic lakes (Egli, 2004b). Moreover, the production of bacterial magnetite can be fostered by the input of nutri-ents (Egli, 2004b). Magnetotactic bacteria producing greigite prefer reducing conditions, and greigite magnetosomes have a higher potential for preservation under sulfidic conditions (Chang et al, 2014;Vasiliev et al, 2008).…”

Section: Bacterial Magnetite In Lake Ohrid Sediments?mentioning

confidence: 99%

“…However, in addition to the detrital magnetic inventory, magnetic minerals form in the course of syn-and post-sedimentary processes. Magnetotactic bacteria living in the oxic-anoxic transition zone in the topmost sediments utilize magnetic minerals, and can produce either magnetite or greigite intracellularly (Egli, 2004b;Roberts et al, 2012;Snowball et al, 2002;Vali et al, 1989). Furthermore, iron-reducing bacteria may induce the authigenic precipitation of magnetite (e.g., Bell et al, 1987;Frankel and Bazylinski, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

et al. 2016

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Abstract. The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial-interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before ∼ 320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe / Ca ratios in the sediments.While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high-to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial-interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial-interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes.

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Section: Bacterial Magnetite In Lake Ohrid Sediments?mentioning

confidence: 99%

Section: Bacterial Magnetite In Lake Ohrid Sediments?mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

et al. 2016

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“…[4] Although simple scalar properties such as bulk susceptibility may have paleoenvironmental significance [Heller et al, 1993;Maher et al, 1994;Maher and Thompson, 1995], in most cases it is far more informative to look at spectral properties such as the coercivity distribution [Dunlop, 1972[Dunlop, , 1986Robertson and France, 1994;Heslop et al, 2002;Egli, 2003Egli, , 2004aEgli, , 2004b. Preisach analysis and its descendant FORC analysis go a step further by mapping out a distribution of ''hysteron'' properties H c and H u which are interpreted as coercivity and interaction field, respectively [Roberts et al, 2000;Pike et al, 2001;Newell, 2005].…”

Section: Introductionmentioning

confidence: 99%

Characterizing the superparamagnetic grain distribution f(V, H_k) by thermal fluctuation tomography

et al. 2006

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[1] In 1965, D. J. Dunlop showed that the joint distribution of particle volumes and microcoercivities f(V, H k0 ) can be determined for magnetically monomineralic, thermally stable single-domain (SSD) ensembles by taking advantage of the joint temperature and field dependence of relaxation time. We have developed a procedure that follows Dunlop's strategy to obtain f(V, H k0 ) for ensembles containing both superparamagnetic and SSD grains, based on backfield remanence curves measured over a range of temperatures. Each point on the derivative curves represents the integrated contribution from grains that lie along a corresponding blocking contour on the Néel plot. A suitable set of such line integral samples can be used to reconstruct the f(V, H k0 ) distribution using the methods of tomographic imaging. Samples of the basal Tiva Canyon Tuff have narrow size distributions of elongate Ti-poor titanomagnetite. Tomographic inversion of the low-temperature backfield spectra yield sharply peaked f(V, H k0 ) distributions, from which we calculate modal grain dimensions in good agreement with those observed by transmission electron microscopy. Analysis of synthetic samples containing bimodal populations clearly distinguishes the two modes. Because our simplified forward calculations incompletely account for the effects of orientation distribution, the width of the coercivity distribution at each temperature is underestimated, and consequently, the inverse calculations yield grain distributions that are overly broad. Frequency-and temperature-dependent susceptibilities calculated for the inverted f(V, H k0 ) distributions accord fairly well with measured susceptibilities for the weakly interacting Tiva Canyon samples, less well for a moderately interacting paleosol specimen, and poorly for a strongly interacting ferrofluid.Citation: Jackson, M., B. Carter-Stiglitz, R. Egli, and P. Solheid (2006), Characterizing the superparamagnetic grain distribution f(V, H k ) by thermal fluctuation tomography,

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“…The earliest deposits in-filling the Basin are the conglomerates and sandstones of the Hacıbekir Group (Kürtkőyü and Yenikőy Formations), which is generally accepted as Early Miocene in age (Seyitoğlu, 1997, Westaway et al, 2003, 2004. This Group has a restricted outcrop within the study area and comprises coarse grade and angular gravels interpreted Page 6 of 61 as alluvial fan facies derived from the topographic highs of the metamorphic and ophiolitic hills of the Early Miocene.…”

Section: Pre-quaternary Stratigraphy and Neotectonics In The Selendi mentioning

confidence: 99%

The Gediz River fluvial archive: A benchmark for Quaternary research in Western Anatolia

Maddy

Veldkamp

Demi̇r

et al. 2017

Quaternary Science Reviews

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Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTThe Gediz River, one of the principal rivers of Western Anatolia, has an extensive Pleistocene fluvial archive that potentially offers a unique window into fluvial system behaviour on the western margins of Asia during the Quaternary. In this paper we review our work on the Quaternary Gediz River Project (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) and present new data which leads to a revised stratigraphical model for the Early Pleistocene development of this fluvial system.In previous work we confirmed the preservation of eleven buried Early Pleistocene fluvial terraces of the Gediz River (designated GT11, the oldest and highest, to GT1, the youngest and lowest) which lie beneath the basalt-covered plateaux of the Kula Volcanic Province. Deciphering the information locked in this fluvial archive requires the construction of a robust geochronology. Fortunately, the Gediz archive provides ample opportunity for ageconstraint based upon age estimates derived from basaltic lava flows that repeatedly entered the palaeo-Gediz valley floors. In this paper we present, for the first time, our complete dataset of 40 Ar/ 39 Ar age estimates and associated palaeomagnetic measurements. These data, which can be directly related to the underlying fluvial deposits, provide age constraints critical to our understanding of this sequence.The new chronology establishes the onset of Quaternary volcanism at ~1320ka (MIS42). This volcanism, which is associated with GT6, confirms a pre-MIS42 age for terraces GT11-GT7. Evidence from the colluvial sequences directly overlying these early terraces suggests that they formed in response to hydrological and sediment budget changes forced by climatedriven vegetation change. The cyclic formation of terraces and their timing suggests they represent the obliquity-driven climate changes of the Early Pleistocene. By way of contrast the GT5-GT1 terrace sequence, constrained by a lava flow with an age estimate of ~1247ka, span the time-interval MIS42 -MIS38 and therefore do not match the frequency of climate change as previously suggested. The onset of volcanism breaks the simple linkage of terracing to climate-driven change. These younger terraces more likely reflect a localized terracing process triggered by base level changes forced by volcanic eruption and associated reactivation of pre-existing faults, lava dam construction, landsliding and subsequent lavadammed lake drainage.Establishing a firm stratigraphy a...

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Characterization of individual rock magnetic components by analysis of remanence curves. 3. Bacterial magnetite and natural processes in lakes

Cited by 140 publications

References 55 publications

Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

Characterizing the superparamagnetic grain distribution f(V, H_k) by thermal fluctuation tomography

The Gediz River fluvial archive: A benchmark for Quaternary research in Western Anatolia

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Characterization of individual rock magnetic components by analysis of remanence curves. 3. Bacterial magnetite and natural processes in lakes

Cited by 140 publications

References 55 publications

Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

Characterizing the superparamagnetic grain distribution f(V, Hk) by thermal fluctuation tomography

The Gediz River fluvial archive: A benchmark for Quaternary research in Western Anatolia

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Product

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Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

Characterizing the superparamagnetic grain distribution f(V, H_k) by thermal fluctuation tomography