Alternating field demagnetization of rocks, and the problem of gyromagnetic remanence

Dankers, P.; Zijderveld, J.D.A.

doi:10.1016/0012-821x(81)90029-7

Cited by 73 publications

(79 citation statements)

References 5 publications

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“…This was manifested as a dramatic shallowing of the NRM directions and increase in moment during static three-axis AF treatment: GRM is acquired perpendicularly to the final (in this case, vertical) AF axis. Fortunately, GRM-correction methods (Dankers and Zijderveld 1981;Stephenson 1993;Hu et al 1998), like measuring the moment after each uniaxial AF treatment, mitigate these effects and retrieve origin-trending magnetization (Fig. 1).…”

Section: Scarcity Of Materials and Implications For Demagnetization Mementioning

confidence: 98%

Paleomagnetic Records of Meteorites and Early Planetesimal Differentiation

et al. 2009

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The large-scale compositional structures of planets are primarily established during early global differentiation. Advances in analytical geochemistry, the increasing diversity of extraterrestrial samples, and new paleomagnetic data are driving major changes in our understanding of the nature and timing of these early melting processes. In particular, paleomagnetic studies of chondritic and small-body achondritic meteorites have revealed a diversity of magnetic field records. New, more sensitive and highly automated paleomagnetic instrumentation and an improved understanding of meteorite magnetic properties and the effects of shock, weathering, and other secondary processes are permitting primary and secondary magnetization components to be distinguished with increasing confidence. New constraints on the post-accretional histories of meteorite parent bodies now suggest that, contrary to early expectations, few if any meteorites have been definitively shown to retain records of early solar and protoplanetary nebula magnetic fields. However, recent studies of pristine samples coupled with new theoretical insights into the possibility of dynamo generation on small bodies indicate that some meteorites retain records of internally generated fields. These results indicate that some planetesimals formed metallic cores and early dynamos within just a few million years of solar system formation.

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Section: Scarcity Of Materials and Implications For Demagnetization Mementioning

confidence: 98%

Paleomagnetic Records of Meteorites and Early Planetesimal Differentiation

et al. 2009

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“…GRM can become stronger than the starting NRM. To minimize the GRM during AF demagnetization, we followed the protocol of Dankers and Zijderveld (1981). The samples are statically AF demagnetized along three orthogonal axes at a certain AF level and only the component parallel to the last demagnetization axis is used to calculate the NRM vector.…”

Section: Methodsmentioning

confidence: 99%

A Greigite-Based Magnetostratigraphic Time Frame for the Late Miocene to Recent DSDP Leg 42B Cores from the Black Sea

et al. 2016

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Throughout the Late Neogene, the Black Sea experienced large paleoenvironmental changes, switching between (anoxic) marine conditions when connected to the Mediterranean Sea and (oxic) freshwater conditions at times of isolation. We create a magnetostratigraphic time frame for three sites drilled during Deep Sea Drilling Project (DSDP) Leg 42B to the Black Sea (drilled in 1975). At the time, magnetostratigraphic dating was impossible because of the presence of the little understood iron sulfide mineral greigite (in sediments a precursor to pyrite) as magnetic carrier. Our rock-magnetic results indicate that only anoxic conditions result in poor magnetic signal, likely as a result of pyrite formation in the water column rather than in the sediment. The magnetostratigraphic results indicate that Hole 379A, drilled in the basin center, has a continuous sedimentary record dating back to 1.3 Ma. Hole 380/380A is subdivided into three consistent intervals, 0-700 mbsf, 700-860 mbsf, and 860-1075 mbsf. The top unit covers the Pleistocene but the magnetostratigraphy is likely compromised by the presence of mass transport deposits. The middle unit spans between 4.3 and 6.1 Ma and records continuous deposition at ∼10 cm/kyr. The lower unit lacks the independent age constraints to correlate the obtained magnetostratigraphy. Hole 381 is drilled on the Bosporus slope and as a result, hiatuses are common. A correlation to the nearby Hole 380/380A is proposed, but indicates deposits cannot straightforwardly be traced across the slope. Our improved age model does not support the original interpretation based on these cores of a desiccation of the Black Sea during the Messinian salinity crisis.

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“…Since we expected that the sediment may contain greigite, we have taken extra steps in small increments between 25 mT and 40 mT, because for greigite we often find the generation of a Gyroremanent Magnetization (GRM) at fields higher than 40 mT. In order to overcome the problem of gyroremanence during alternating field demagnetization the specifically designed per component demagnetization scheme of Dankers and Zijderveld (1981) was applied. This method involves longer measuring and processing on the robotized system, but tries to eliminate as much as possible the growing GRM component at higher alternating fields.…”

Section: Alternating Field and Thermal Demagnetizationmentioning

confidence: 99%

Paleomagnetic analyses on Badenian–Sarmatian drill cores from the North Carpathian Foredeep (Middle Miocene, Poland)

Sant

Leeuw

Chang

et al. 2015

Biuletyn Państwowego Instytutu Geologicznego

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Abstract. Accurate dating of the Badenian-Sarmatian transition, a boundary between two regional Middle Miocene stages of the semi-isolated Paratethys Sea, is crucial to understand what event caused the corresponding major turnover in faunal assemblage at that point in time. The general opinion is that this event resulted from a sudden isolation of the Eastern Paratethys from ocean water, due to the closure of the Eastern Anatolian seaway to the Indian Ocean, but it remains debated if the final isolation had a tectonic or climatic cause. This pilot study presents paleomagnetic analyses of two drill cores from the North Carpathian Foredeep in Poland that straddle the Badenian-Sarmatian transition. Rock magnetic experiments, including thermomagnetic runs in air on a Curie balance, and hysteresis measurements on a MicroMag, indicate that the dominant magnetic carrier is the iron sulphide greigite. This is in agreement with the observed gyroremanence obtained during alternating field demagnetization above 40 mT. Alternating field and thermal demagnetization results are in good agreement and show a weak, mixed-polarity, signal for most of the Badenian, rapidly shifting to a much stronger and dominantly normal polarity signal in the Sarmatian part of the cores. First order reversal curves diagrams indicate that the greigite in the Sarmatian part is clearly of diagenetic origin, it thus most likely concerns a secondary overprint by the present-day field that cannot be used for magnetostratigraphic correlations. We conclude that the Paratethys-wide paleoenvironmental change that occurred at the Badenian-Sarmatian transition had probably also created different conditions for the formation and/or preservation of magnetic minerals.Key words: Badenian-Sarmatian boundary, paleomagnetic dating, Northern Carpathian Foredeep.Abstrakt. Dokładne datowanie przejścia baden-sarmat, granicy dwóch regionalnych pięter środkowego miocenu na terenie częściowo izolowanego morza Paratetydy, jest istotne dla zrozumienia przyczyny wyraźnej zmiany zespołów faunistycznych, która towarzyszyła temu wydarzeniu. Według powszechnie akceptowanych poglądów wydarzenie to było wynikiem nagłego odcięcia obszaru Paratetydy Wschodniej od otwartego oceanu wskutek zamknięcia cieśnin na terenie wschodniej Anatolii, które stanowiły łącznik z Oceanem Indyjskim. Obecnie przedmiotem dyskusji jest tektoniczna lub klimatyczna przyczyna tego wydarzenia. Paleomagnetyczne badania pilotowe rdzeni z dwóch otworów wiertniczych, położonych w północnej części zapadliska przedkarpackiego na terenie Polski, dotyczą przejścio-wej, badeńsko-sarmackiej sukcesji osadowej. Badania petromagnetyczne (w tym analizy termomagnetyczne na wadze Curie oraz histerezy na instrumencie MicroMag) wskazują, że dominującym minerałem magnetycznym jest siarczek żelaza -greigit, co potwierdza obecność składowej giromagnetycznej podczas rozmagnesowywania próbek zmiennym polem magnetycznym powyżej 40 mT. Wyniki polowej i termicznej demagnetyzacji są zgodne i wskazują na słaby sygnał, o mieszanej pol...

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Alternating field demagnetization of rocks, and the problem of gyromagnetic remanence

Cited by 73 publications

References 5 publications

Paleomagnetic Records of Meteorites and Early Planetesimal Differentiation

Paleomagnetic Records of Meteorites and Early Planetesimal Differentiation

A Greigite-Based Magnetostratigraphic Time Frame for the Late Miocene to Recent DSDP Leg 42B Cores from the Black Sea

Paleomagnetic analyses on Badenian–Sarmatian drill cores from the North Carpathian Foredeep (Middle Miocene, Poland)

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