Magnetic Properties of Coring Samples from Aceh Basin West Off Sumatera Island

Magnetic Polarity ◽

Reverse Polarity ◽

Geologic Time ◽

The Third ◽

Geologic Time Scale ◽

The Last Glacial Maximum ◽

The Last Glacial

Three oriented core samples was taken by Japanese MIRAI Research Vessel in Aceh Basin west of the Sumatera Island. 927 small box samples from 3 coring samples was measure. Core bottom ages of three cores are in the last glacial maximum (around 19 kyBP). We measured Natural Remanent Magnetization (NRM), NRM after Alternating Field Demagnetization up to 800 Oe. Measurement of NRM have done by 2G Enterprice Squid, Isothermal Remanent Magnetization (IRM) and Anhysteretic Remanent Magnetization (ARM) on Paleomagnetic Laboratory of Geological Survey of Japan. Result of NRM after Alternating Field Demagnetization shows that there are reverse polarizaty magnetizations. This reverse polarity seems not usual since in Geologic Time Scale 1989 showed that the first reversal polarity was between Brunches Normal Epoch and Jaramillo Epoch beginning at 0.75 Ma There are some possibility of reverse polarity events contained in the three cores mentioned above. The first possibility is the result of the tsunami so that the sediment that settles on the Aceh Basin was a sediment that remain turbid flows that enable magnetic recording on magnetic sediment did not follow directions when he formed so that it seems a polarity reverse polarity when only superficial. The second possibility is indeed occurs under reverse polarity at age 700.000 years. Research in Argentina, South America show that between 11 thousand to two thousand years ago there was an excursion from the magnetic polarity produces some reverse polarity at the time (Nami, 1999). The third possibility was circular variation magnetic.

Magnetostratigraphy of U-Pb–dated boreholes in Svalbard, Norway, implies that magnetochron M0r (a proposed Barremian-Aptian boundary marker) begins at 121.2 ± 0.4 Ma

Geology ◽

10.1130/g48591.1 ◽

2021 ◽

Author(s):

Yang Zhang ◽

James G. Ogg ◽

Daniel Minguez ◽

Mark W. Hounslow ◽

Snorre Olaussen ◽

...

Keyword(s):

Spreading Rate ◽

Magnetic Polarity ◽

Stratigraphic Correlation ◽

Geologic Time ◽

Oceanic Spreading ◽

M Sequence ◽

Geologic Time Scale ◽

Age Model ◽

Oceanic Basalts ◽

Radioisotopic Dating

The age of the beginning of magnetic polarity Chron M0r, a proposed marker for the base of the Aptian Stage, is disputed due to a divergence of published radioisotopic dates and ambiguities in stratigraphic correlation of sections. Our magnetostratigraphy of core DH1 from Svalbard, Norway, calibrates a bentonite bed, dated by U-Pb methods to 123.1 ± 0.3 Ma, to the uppermost part of magnetozone M1r, which is ~1.9 m.y. before the beginning of Chron M0r. This is the first direct calibration of any high-precision radioisotopic date to a polarity chron of the M sequence. The interpolated age of 121.2 ± 0.4 Ma for the beginning of Chron M0r is younger by ~5 m.y. than its estimated age used in the Geologic Time Scale 2012, which had been extrapolated from radioisotopic dates on oceanic basalts and from Aptian cyclostratigraphy. The adjusted age model implies a commensurate faster average global oceanic spreading rate of ~12% during the Aptian–Santonian interval. Future radioisotopic dating and high-resolution cyclostratigraphy are needed to investigate where to expand the mid-Jurassic to earliest Cretaceous interval by the required ~4 m.y.

Evidence of Single-Domain Magnetite in the Michikamau Anorthosite

Canadian Journal of Earth Sciences ◽

10.1139/e71-036 ◽

1971 ◽

Vol 8 (3) ◽

pp. 361-370 ◽

Cited By ~ 49

Author(s):

G. S. Murthy ◽

M. E. Evans ◽

D. I. Gough

Keyword(s):

Remanent Magnetization ◽

Theoretical Models ◽

Single Domain ◽

Mineral Separation ◽

Domain Configuration ◽

Plagioclase Felspar ◽

Magnetite Particles ◽

Theoretical Evidence

The Michikamau anorthosite possesses very stable natural remanent magnetization, some of which resists alternating fields up to 1800 Oe. The rock contains two types of opaque grains, fine opaque needles of order 10 × 0.5 μ in the plagioclase felspar, and large equidimensional magnetite particles. Ore microscope studies suggest, but do not establish, that the needles are composed of magnetite. Saturation isothermal remanence and thermal demagnetization studies indicate magnetite as the carrier of remanent magnetization. In order to distinguish the effects of the large grains from those of the needles, mineral separation was used to show that an artificial specimen of essentially pure plagioclase had very similar isothermal remanent magnetization properties to the whole rock. Both indicated magnetite as the magnetic mineral. Thermoremanent properties of the separated mineral fractions indicated magnetite as the dominant magnetic constituent but showed some evidence of laboratory-produced hematite. Theoretical models of grains elongated along [111] and [110] axes are used to show that magnetite needles can exist in stable single-domain configuration in the size and shape ranges of the needles observed in the Michikamau anorthosite. There is thus considerable experimental and theoretical evidence for the conclusion that the stable remanent magnetization of the Michikamau anorthosite is carried by fine single–domain needles of magnetite in the plagioclase felspar.

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

Magnetic characteristics of Luna 16 and 20 samples

10.1098/rsta.1977.0005 ◽

1977 ◽

Vol 284 (1319) ◽

pp. 151-156 ◽

Cited By ~ 1

Keyword(s):

Grain Size ◽

Iron Content ◽

Remanent Magnetization ◽

Magnetic Behaviour ◽

Heavy Fraction ◽

Magnetic Characteristics ◽

Iron Particles ◽

Rock Fragments

The natural remanent magnetization of rock fragments L2015,3,1 and L2015,3,11 was found to be < 3.5 x 10 -7 and < 40 x 10 -6 G cm 3 g -1 respectively. The former sample, from isothermal remanent magnetization (i.r.m.) measurements, contained very little iron, while the latter sample had a much higher iron content and exhibited i.r.m. characteristics similar to breccia samples from Apollo missions. Susceptibility and i.r.m. measurements have shown that Luna 16 fines contain about four times as much iron as Luna 20 samples and that the light fractions from the density separations contain about twice as much iron as the heavy fraction. Like the Apollo fines, the magnetic behaviour of Luna 16 and 20 fines is dominated by small iron particles, most of which are superparamagnetic and of grain size less than about 13 nm.

Application of the pseudo-Thellier technique to a paleomagnetic record from lake El Trébol (Patagonia, Argentina)

Geofísica Internacional ◽

10.22201/igeof.00167169p.2008.47.4.2144 ◽

2008 ◽

Vol 47 (4) ◽

pp. 319-327

Author(s):

C. S. G. Gogorza ◽

S. Torcida ◽

A. M. Sinito ◽

M. A. E. Chaparro

Keyword(s):

Magnetic Susceptibility ◽

Error Estimates ◽

Sediment Core ◽

Standard Method ◽

Remanent Magnetization ◽

Reasonable Agreement ◽

Low Field ◽

Relative Paleointensity

The pseudo-Thellier technique was applied to obtain relative paleointensity determinations using a sediment core from Lake El Tre?bol (Patagonia, Argentina). Measurements of intensity of natural remanent magnetization left (NRMleft) after AF demagnetization versus intensity of anhysteric remanent magnetization gained (ARMgained) at the same peak were carried out on a set of samples. Two versions of a jackknife resampling scheme were used to get error estimates on the paleointensity. The pseudo-Thellier paleointensity records were compared with the authors previous results where the remanent magne- tization at 20mT (NRM20mT) has been normalized using the anhysteric remanent magnetization at 20mT (ARM20mT), the satu- ration of the isothermal remanent magnetization at 20mT (SIRM20mT) and the low field magnetic susceptibility (k) (Gogorza et al., 2006). The pseudo-Thellier record shows a reasonable agreement with the standard method of normalization (NRM20mT/ ARM20mT).

Preliminary absolute paleointensity estimation from a single volcanic-glass grain extracted from an unwelded pyroclastic flow

10.5194/egusphere-egu2020-3242 ◽

2020 ◽

Author(s):

Yuhji Yamamoto ◽

Hiromi Takeda ◽

Masahiko Sato ◽

Hiroshi Kawabata

Keyword(s):

Pyroclastic Flow ◽

Remanent Magnetization ◽

Volcanic Glass ◽

Volcanic Eruptions ◽

Primary Component ◽

Pyroclastic Flows ◽

Inflection Points ◽

Stable Characteristic

Many pyroclastic flows are distributed around Japan. They usually involve volcanic-glass grains. These grains are considered to form at the timing of volcanic eruptions and are expected to have magnetic inclusions consisting of tiny single (titano)magnetites with recording the paleomagnetic field. We have extracted single volcanic-glass grains of pumice-type with a diameter of 0.60-0.84 mm from an unwelded part of the Ito pyroclastic flow deposits (A-Ito, 26-29 ka; Machida and Arai, 2003), Kyusyu, Japan. A series of rock- and paleomagnetic measurements have been made on the grains.Sixty-seven out of 88 grains had detectable intensities of natural remanent magnetization. Some of such grains were further investigated. Results of low-temperature magnetometry exhibited inflection points at 105-120 K, suggesting magnetite as a main remenence carrier. Stepwise alternating field demagnetization revealed an existence of stable characteristic remanence (ChRM) which was interpreted to be a primary component.&#160;Tsunakawa-Shaw method (Tsunakawa and Shaw, 1994; Yamamoto et al., 2003), one of the latest absolute paleointensity (API) techniques to date, was applied to selected grains having stable ChRMs. On the application we newly included measurements related to an isothermal remanent magnetization (IRM). Four successful results were obtained by an adoption of IRM corrections, giving an average API value of about 25 &#956;T. This corresponds to a virtual axial dipole moment (VADM) of about 50 ZAm2, which is consistent with the contemporaneous VADM of the sedimentary record (PISO-1500; Channell et al., 2009).&#160;

Siliceous subglacial deposits: archives of subglacial processes during the Last Glacial Maximum

Journal of Glaciology ◽

10.1017/jog.2021.42 ◽

2021 ◽

pp. 1-8

Author(s):

Shalev Siman-Tov ◽

Terrence Blackburn ◽

Bernard Hallet ◽

Matthew A. Coble ◽

Emily E. Brodsky

Keyword(s):

Isotopic Analysis ◽

Rock Fragment ◽

Isotopic Data ◽

Geologic Time ◽

Rock Interface ◽

The Last Glacial Maximum ◽

Siliceous Deposit ◽

Detailed Chemical ◽

The Last Glacial

Abstract We report detailed chemical and isotopic data from a subglacial siliceous deposit on andesitic bedrock recently exposed by glacier retreat. Whereas a single, <1 μm, Si-rich layer covers the highly polished bedrock on the up-glacier (stoss) surfaces, distinct, lithified deposits commonly occur at the lee of small bedrock protuberances, on a scale <0.1 meter. The deposit is millimeters in thickness and consists of laminae tens to hundreds microns thick that differ from one another in color, rock-fragment abundance and chemical composition. Ca-rich laminae that are sufficiently enriched in uranium (~2–50 ppm) to permit U-series isotopic analysis suggest that the subglacial deposit formed 10–20 ka, much earlier than previously assumed. We conclude that (1) the siliceous deposit persisted for at least 10 000 years despite the intervening erosion and weathering, (2) distinct episodes of formation due to significant changes in hydrology and water chemistry are recorded in the deposit, and (3) a siliceous slurry may have existed at the ice-rock interface and influenced the local friction. This work reinforces earlier findings that subglacial chemical deposits can form and persist on geologic time scales and may have implications for the role of the cryosphere in the Earth's geochemical cycles and climate system.

ARCHAEOMAGNETIC STUDIES IN KILNS FROM N. GREECE

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.11380 ◽

2017 ◽

Vol 43 (4) ◽

pp. 1888 ◽

Cited By ~ 2

Author(s):

E. Aidona ◽

D. Kondopoulou ◽

M. Alexandrou ◽

N. Ioannidis

Keyword(s):

Magnetic Field ◽

Remanent Magnetization ◽

Archaeological Sites ◽

Thermomagnetic Analysis ◽

Intensity Measurements ◽

Magnetic Carriers ◽

Characteristic Component

Archaeomagnetism combines the magnetic properties of baked materials with Archaeology. The archaeomagnetic method can be applied to any kind of permanent - in situ or displaced- burnt structures, such as kilns, ovens, hearths, burnt floors, tiles, bricks and pottery fragments, the latter for intensity measurements only. In this study we present the latest archaeomagnetic results from archaeological sites which are distributed in N. Greece (Polymylos, Sani, Thesssaloniki). The Natural Remanent Magnetization (NRM) and the magnetic susceptibility of the samples have been initially measured. The samples have been subjected to magnetic cleaning (AF and Thermal demagnetizations) and this procedure revealed the characteristic component of the ancient magnetic field. Rock magnetic experiments such as acquisition of the Isothermal Remanent Magnetization (IRM) and thermomagnetic analysis have been performed in pilot samples in order to identify the main magnetic carriers. Finally the secular variation curves for Greece and the SCHA.DIF.3K model were used in order to date these archaeological structures. This dating improved or modified the estimated archaeological ages.

Paleomagnetism of Archean rocks from northwestern Ontario: V. Poohbah Lake alkaline complex, Quetico Subprovince

Canadian Journal of Earth Sciences ◽

10.1139/e85-003 ◽

1985 ◽

Vol 22 (1) ◽

pp. 27-38 ◽

Cited By ~ 9

Author(s):

David J. Dunlop

Keyword(s):

Remanent Magnetization ◽

Reverse Polarity ◽

Alkaline Complex ◽

Field Reversal ◽

Polar Wander ◽

Fine Grained ◽

Rock Types ◽

Northwestern Ontario ◽

Normal Polarity

The Poohbah Lake alkaline complex is a late synkinematic Kenoran pluton in the Quetico gneiss belt of the western Superior Province. Three units of the complex, porphyritic syenite (PS), malignite (M: a nepheline–clinopyroxene–K-feldspar rock), and hornblende syenite (HS), as well as baked Archean schists near the intrusive contact, have a predominantly reverse-polarity R magnetization with mean direction D = 198° I = −22.5° (k = 62, α95 = 5°, N = 13 sites) and a paleopole at 60°E, 50.5°N. Pyrrhotite and coarse primary magnetite are carriers of the R remanence. PS, M, and biotite pyroxenite (BP) exhibit also a predominantly normal N magnetization carried by fine-grained, probably secondary magnetite. N is systematically steeper than R: its mean direction is D = 359.5° I = +55.5° (k = 28, α95 = 8°, N = 13 sites) with a paleopole at 90°E, 77.5°N. R and N do not record an asymmetric field reversal, since reverse-polarity N vectors and normal-polarity R vectors are occasionally found. R resembles in polarity and direction the natural remanent magnetization (NRM) of the 2630 Ma Matachewan diabase. It is probably the primary NRM of the Poohbah Lake pluton, with an age of about 2650 Ma in approximate agreement with the K/Ar isochron age of 2700 ± 25 Ma. N resembles in polarity and direction NRM's from the 2580 Ma Shelley Lake granite and the late Archean Burchell Lake granite. It is probably a secondary NRM about 2550 Ma in age, as suggested by updated K/Ar mica ages. The characteristic NRM of HS samples and secondary magnetizations in other rock types have poles on the Grenville Track of the polar wander path but there is no evidence for Grenvillian-age events in the area.