Rock Magnetic Characteristics Research Articles

Magnetostratigraphy of the Permian–Triassic Boundary in the Lower Reaches of the Vetluga River, East European Platform, Nizhny Novgorod Region

We present the results of detailed paleomagnetic studies of six Permian-Triassic boundary sections in the central part of the East European Platform, located in the lower reaches of the Vetluga River: Astashikha, Voskresenskoe, Znamenskoe, Prudovka, Sosnovka, and Sukhoborka. The paleomagnetic data, which meet the modern quality standards for laboratory processing, together with the results of biostratigraphic studies, allow for the development and substantiation of magnetostratigraphic scales for each section, as well as for their correlation and the construction of a magnetic polarity scale for the Permian-Triassic sedimentary complex of the Vetluga River. Rock-magnetic characteristics are determined for each of the studied sections, and paleomagnetic poles of the East European Platform are calculated for the Late Permian and Permian-Triassic boundary.

Late Pleistocene and Holocene Sedimentation in the glacial Lake Sosednee, Magadan region

Lake Sosednee is located in the Yagodninsky district of the Magadan region. It was formed in the Late Pleistocene around 22,500 cal. years ago. The rock magnetic, geochemical, palynological, and mineralogical characteristics of the sediments of four cores, as well as moraine, and various grain size fractions of the hillslope sediments were studied. It has been established that the geochemical and rock magnetic properties of sediments from lake Sosednee reflect different sedimentation conditions, changing from the cold climate of the Late Pleistocene to the warm climate of the Holocene. In the lower part of the core, authigenic (hemogenic) formation of iron sulfides, including magnetic ones, was revealed. According to the rock magnetic and geochemical data, the Younger Dryas was identified, the end of which corresponds to the Pleistocene–Holocene boundary.

Red clays indicate sub-aerial exposure of the Rio Grande Rise during the Eocene volcanic episode

Autonomous underwater vehicle (AUV) mapping of the western Rio Grande Rise (RGR), South Atlantic, and subsequent exploration and photography of horizontal lava flows exposed in near vertical, faulted escarpments, showed occurrences of red clays/weathered volcanic tops trapped between successive alkaline lava flows. These red clays indicate a hiatus in successive volcanic eruptions. Here, we report detailed mineralogical, geochemical, and rock magnetic characteristics of one such distinct red clay dredged from ~ 650 m water depth in the western RGR. The mineral constituents of the red clay are kaolinite, magnetite, oxidized magnetite (/maghemite), hematite, and goethite, with biogenic calcite and halite occupying voids or precipitated on the surface of the red clay. The chemical index of alteration (CIA) has a value of 93, showing that red clay is a product of extreme chemical weathering of the lava flows. The alkaline volcanic rocks recovered from nearby show an age of ~ 44 Ma, indicating an Eocene age for the volcanism. We show that the red clays are a product of sub-aerial chemical weathering of these Eocene volcanic rocks, in a warm-wet climate, before the thermal subsidence of the RGR to its modern-day bathymetric depth.

Magma storage conditions beneath Krakatau, Indonesia: insight from geochemistry and rock magnetism studies

Understanding the evolution of magma storage conditions on volcanoes which have had more than one caldera-forming eruption (CFE) is important to know about past and present conditions, as a key to forecast future potential hazards. Krakatau volcano is characterized by cyclic phases of growth and destruction of the edifice. A volcanostratigraphic study identified three eruptive periods: Old Krakatau, Young Krakatau, and Anak Krakatau. The Old and Young Krakatau periods ended with the first and second CFE respectively. Due to its permanent activity and edifice evolution, Krakatau poses a high risk on the surrounding inhabited islands. In this study, we combined geochemistry, rock magnetic, and petrology to infer the evolution of magma storage conditions from Old to Anak Krakatau periods. This study is the first to report on the chemical and rock magnetic characteristics, as well as storage system conditions of Old Krakatau and its relation to the ongoing evolution of Krakatau. Our data show that: 1) Old and Young Krakatau magma storage regions are shallow (within the upper 3 km), contain more differentiated magmas, from which the Old Krakatau magmas may be less oxidized and had lower temperatures than Young Krakatau; 2) Anak Krakatau magma storage is deeper (up to 26 km), less differentiated, and erupted hotter but more reduced compared to Old and Young Krakatau. The Old and Young Krakatau lavas were the products of pre-CFE and their chemical characteristics are included at maturation phase, whereas the Young Krakatau pumice samples were the product of the second CFE. Lastly, the post-second CFE activity of AK is currently in an incubation phase and represented by mafic products of frequent and small eruptions. Knowing that the volcano has experienced maturation and CFE phases in the past, the current AK may evolve to those phases in the future.

Cyclostratigraphic Analysis Results of the Rock Magnetic and Geochemical Characteristics of Belogrodni Formation Stratotype (Danian Stage in the Volga Right Bank Area Near Saratov)

Cyclostratigraphic Analysis Results of the Rock Magnetic and Geochemical Characteristics of Belogrodni Formation Stratotype (Danian Stage in the Volga Right Bank Area Near Saratov)

Rock magnetic characteristics of the Wenchuan-Maoxian fault zone of the Longmen Shan fault and its earthquake faulting characteristics

Rock magnetic characteristics of the Wenchuan-Maoxian fault zone of the Longmen Shan fault and its earthquake faulting characteristics

Результаты рекогносцировочных магнитостратиграфических исследований палеоцена в южной части Саратовского Правобережья

The results of rock-magnetic and paleomagnetic studies of two sections of the Lower Syzran subformation (Paleocene) of the Saratov Right Bank – the Syrt Mountain (Nizhnyaya Bannovka village) and Lysaya Gora (Saratov city) are presented. For the first time the possibility of obtaining paleomagnetic data on the Paleocene of the Volga region and their use for magnetostratigraphic purposes despite the partial remagnetization of rocks has been established. The prospects of using rock-magnetic characteristics of deposits for detailed correlations of sections and sedimentological reconstructions are demonstrated.

Rock-magnetic characteristics and mechanisms of the Titel loess-paleosol sequence in northern Serbia since late Middle Pleistocene

Rock-magnetic characteristics and mechanisms of the Titel loess-paleosol sequence in northern Serbia since late Middle Pleistocene

Magnetostratigraphy of the Triassic Moenkopi Formation From the Continuous Cores Recovered in Colorado Plateau Coring Project Phase 1 (CPCP‐1), Petrified Forest National Park, Arizona, USA: Correlation of the Early to Middle Triassic Strata and Biota in Colorado Plateau and Its Environs

AbstractThe Colorado Plateau Coring Project Phase 1 (CPCP‐1) acquired three continuous drill cores from Petrified Forest National Park (PFNP), Arizona, U.S.A., two of which (CPCP‐PFNP13‐1A and CPCP‐PFNP13‐2B) intersected the Upper Triassic Chinle Formation, Lower(?)‐Middle Triassic Moenkopi Formation (MF) and Permian Coconino Sandstone. We examined both cores to construct a high‐resolution magnetostratigraphy of MF strata, and progressive demagnetization data yield well‐defined, interpretable paleomagnetic results. Each lithostratigraphic member of the MF (Wupatki, Moqui, and Holbrook members) contains authigenic and detrital hematite as the dominant magnetic carrier with distinguishing rock magnetic characteristics. Magnetostratigraphy of MF strata in both CPCP‐1 cores consists of six normal and six reverse polarity magnetozones, from the youngest to the oldest, MF1n to MF6r. Recent single‐crystal chemical abrasion–thermal ionization mass spectrometry (CA‐TIMS) U‐Pb data from a sample in magnetozone MF1n yield a latest Anisian/earliest Ladinian (241.38 ± 0.43 Ma) age. Correlation of the CA‐TIMS‐calibrated magnetostratigraphy with the astronomically tuned polarity timescale for the Middle Triassic deep‐marine Guandao (GD) section of South China ties the magnetozone MF1n with GD8 and MF6r with GD2r, and implies that the MF spans, at most, the earliest Anisian (Aegean) to latest Anisian (Illyrian)/earliest Ladinian stages (ca. 246.8 to 241.5 Ma). This age estimate for the MF suggests that the timespan of the regional, pre‐Norian disconformity is about 17 Ma, which demonstrates that MF vertebrate fossil assemblages in east‐central Arizona are millions of years (minimally 3–4 Ma) younger than previously suggested and are all Anisian in age, with no indications of substantial hiatuses in the MF section.

Rock magnetic and palaeomagnetic studies of loess-palaesol sections — Lower Palaeolithic sites within the Southern Bug Valley (Medzhybizh, Holovchyntsi)

Combined rock magnetic and palaeomagnetic studies of loess-soil sections — Lower Paleolithic sites in the valley of the Southern Bug (Medzhybizh, Holovchintsi) — have been performed for the first time in order to determine the suitability of these objects for palaeomagnetic study and the establishment of magnetostratigraphic markers. Investigated sections by rock magnetic characteristics are closest to the sections of the Volynian Upland, and refer to the intermediate «Chinese» type of formation of magnetic properties, with an admixture of the «Alaskan» mechanism. These sections are characterized by a low concentration of ferrimagnetic material, the destruction of the primary sedimentary magnetic texture, which makes them unsuitable for qualitative magnetostratigraphic studies. According to the data of magnetic-mineralogical analysis, the samples are subdivided into three groups: the first group includes samples with new formation at 300 °C, which is associated with iron hydroxides or the presence of organic matter; in the second group, the thermomagnetic curves are not informative, which makes it difficult to determine the minerals-carriers; in some samples, the magnetization carrier is magnetite (with defects or finely dispersed). A zone of normal polarity, probably the Brunhes chron, has been reliably determined in the upper part (G-S7S1 soil) of the Holovchyntsi section. In the lower part of the M-S4 soil unit (MIS 11) at Medzhybizh, the Unnamed geomagnetic event at 430 ky has been detected. The paleomagnetic veracity of the remaining investigated layers is questioned. The analogies for the archaeological assemblages from the lower layers of Medzhybizh-A and Holovchintsi-1 are seen in archaic industries of mode 1, which in southeastern Europe are dated back from 800 ky and older. However, reliable data on the Matuyama—Brunhes boundary and, correspondingly, data on the >780 ky age of any layers with artifacts in the Medzhybizh and Holovchintsi sections were not obtained by the palaeomagnetic studies.

Applicability of Magnetic and Geochemical Characterization Techniques to Assess the Evolution of Estuarine Systems: A Case Study of Gad River Estuary Sediments, Maharashtra

River estuarine samples are a complex repository of terrestrial and nearshore geophysical changes. Sediment core raised from the Gad river estuary, situated in Maharashtra state of India, was analyzed to understand their rock magnetic, particle size and geochemical characteristics. These three parameters are closely related to one another signifying detrital model of deposition, devoid of soft diagenetic changes. The magnetic grain size and particle grain size constraining the domain structure and physical structure respectively, are both in consonance with chemical elements that are amenable largely to physical comminution. The integrated approach of this nature has been tried for the first time on estuarine samples of India. Mineral magnetism utilises the magnetic behaviour of a material to interpret environmental processes acting upon it. The study unraveled two-tier climate-induced modifications to erosional activity, suggesting abrupt change at 20 cm depth in a 45 cm core. The magnetic characteristics are seen to be controlled by the presence of ferrimagnetic minerals. Rock magnetic results (χlf, ARM, SIRM) and Curie temperature reveal that low-coercivity magnetite (and/or titanomagnetite) is the dominant magnetic mineral. χlf is more at the bottom and less at the top. Magnetic grain size is coarse at the top and fine at the bottom. Clay and silt proportion is more at the top of the core and that of sand is more at the bottom. Concentration of detrital geochemical elements like Al, Ti and Cr are less at the top and more at the bottom of the core, corroborated by chemical index of weathering and chemical index of alteration. Thus, it is clear from χlf that magnetic minerals are more at the bottom and so are the detrital minerals like Al, Ti and Cr, along with sand. This reveals energy conditions were vigorous at the time of the deposition of these entities at the bottom, which eased out at the top and are corroborated by the presence of clay and silt, having correspondingly low Al, Ti and Cr with low χlf. Micromorphological features revealed abrasion pits, grooves and bumped edges on sub-angular grains, which indicate moderate transport distance under moderate to low energy conditions revealing terrestrial origin of this material. Thus, similar studies in other estuarine complexes can be used as a proxy to understand monsoonal or environmental changes initiated by neotectonic activity.

Integrated rock magnetic and mineralogical study of the Lower Triassic sedimentary rocks from Spitsbergen

A rock magnetic, mineralogical and Mössbauer spectroscopy study was undertaken on the Lower Triassic sediments from the West Spitsbergen Fold and Thrust Belt (WSFTB) in Svalbard as well as the foreland of this orogen for a thorough recognition of magnetic mineralogy, necessary for a better-constrained interpretation of paleomagnetic results. SEM and Mössbauer spectroscopy indicate the presence of magnetite and pyrrhotite, both most probably of secondary origin but altered clasts of volcanic origin and grains of ilmenite and detrital magnetite are also observed. Thermomagnetic curves of whole-rock samples exhibit paramagnetic behavior whereas ferromagnetic separates indicate the presence of magnetite. IRM component analysis shows three major contributors – magnetite, hematite, and pyrrhotite to the remanence, with ferromagnetic iron oxides the most dominant. Identified ferromagnetic minerals display a wide range of grain-size and magnetic behavior, with the domination of PSD particles. Rock magnetic characteristics of both areas are similar, but sites in the fold belt were most likely remagnetized, whereas those in the foreland carry the primary magnetization. The age of remagnetization was estimated as pre-Eurekan related to rift-controlled Mesozoic extensional phases of the Barents Sea Shelf (Clark et al., 2014) and/or Cretaceous injections of dolerites in the Svalbard Archipelago (Nejbert et al., 2011) as well as early stages of the WSFTB formation. However, Triassic remanence might persist in volcanic lithoclasts and detrital magnetite indicated along the WSFTB. The multicomponent nature of the NRM, displaying a broad range of grain size, might impede the paleomagnetic interpretation of Triassic rocks in Spitsbergen.

Paleo-earthquakes revealed by rock magnetic evidence from the Anxian-Guanxian Fault, Sichuan Province, China

To determine the rock magnetic characteristics of this co-seismic rupture generated by the 2008 Wenchuan earthquake in Sichuan Province, China, we excavated a trench on the Anxian-Guanxian fault. High-resolution magnetic susceptibility and other rock magnetic measurements were conducted on the field section and on samples from the trench. We divided the fault rocks into 8 units according to lithology and measurements of magnetic susceptibility were made on fault rocks within different units, both in the field and in the laboratory. The results demonstrate that the highest magnetic susceptibility occurs in the red gouge (64.08 × 10−6 SI for surface magnetic susceptibility and 30.61 × 10−8 m3/kg for mass magnetic susceptibility), while relatively high magnetic susceptibility occurs in the black gouge (14.31× 10−6 SI for surface magnetic susceptibility and 7.15 × 10−8 m3/kg for mass magnetic susceptibility) compared to the protolith. More detailed magnetic measurements were used to determine the magnetic mineralogy of each unit. The principal mechanism responsible for the high magnetic susceptibility values of the red gouge is the neoformation of magnetite from siderite or pyrrhotite caused by thermal pressurization during the latest earthquakes, which reveals the location of the latest seismic slip zone. By contrast, the magnetic susceptibility values of the black gouge have been reduced by the formation of goethite during weathering. We conclude that although the occurrence of goethite reveals paleo-earthquake, factors such as the oxidation or dissolution of fluids that effect magnetic minerals need further investigation.

Modern Geothermochronological and Paleomagnetic Potential for Solving Mineral Exploration Problems

The paper considers in brief modern paleomagnetic and geochronological methods based on the study of the magnetic properties and isotope composition of rocks and successfully used in international practice in solving urgent applied and fundamental problems in geology, geophysics, and related sciences. The paleomagnetic method is widely used for spatially orienting borehole cores, allows intra- and interbasin correlations of paleontologically barren sedimentary cross sections, and is applied for the age correlation of ore-bearing intrusions and lava strata. Knowledge of the rock magnetic characteristics of rocks makes it possible to create 3D models of the poroperm characteristics of reservoirs of caustobioliths and reconstruct hydrocarbon migration paths. Thermochronological methods are generally used to reconstruct the thermal evolution of sedimentary basins: they make it possible to estimate the temperature and duration of heating of sedimentary and crystalline rock complexes; calculate the value of the geothermal gradient in the past, which is especially important for evaluating the conditions of hydrocarbon generation; reconstruct the tectonic history of sedimentary basins; calculate the thicknesses of eroded deposits; and identify the burial and uplift phases of crustal blocks. It is noted that the integrated use of modern methods and advanced equipment makes it possible to obtain comparable results at the world level. As an example, the results of multidisciplinary research on the Kola Peninsula are presented; they are used as a basis for creating a unique model of the tectonothermal evolution of northeastern Fennoscandia and the Barents Sea shelf. The article presents the resource base and the basic characteristics of the equipment used for the implementation of these methods at Russia’s leading scientific centers, such as Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Kazan Federal University, and St. Petersburg State University. The developed apparatus makes it possible to carry out the whole set of studies considered in this work for the needs of Russia’s mining and energy complexes.

Holocene sedimentation on the distal Amazon Fan/Demerara Abyssal Plain

We have studied the rock magnetic characteristics of 31 multicores and 7 gravity cores from deep-sea sediments of the distal Amazon Fan and Demerara Abyssal Plain. This study has permitted us to delineate the space/time pattern of Holocene physical sedimentation along the northeastern margin of South America associated with the Amazon River sediment plume. The rock magnetic variability is correlatable over the entire study region. This degree of correlation has permitted us to develop a composite picture of Holocene rock magnetic (and overall physical clastic) sedimentation. 26 radiocarbon dates have been combined with the rock magnetic correlations to provide a composite Holocene chronostratigraphy for that variability. We have built isopach maps of overall sedimentation for three windows in the Holocene (3000, 4500, and 7000 calendar years BP). The overall sedimentation in the center of our region is ~5 cm/kyr. But, sedimentation rates are faster closer to the coastline and associated with the distal clastic flux from the Amazon Plume. There is a secondary high in sediment accumulation under the North Brazil Current retroflection. Our maps suggest that the retroflection has been active at the millennial scale for at least the last 7000 years. We estimate that the mid-Holocene (~4.5–9000 calendar years BP) pattern of sedimentation was distinctly different from that of the last few thousand years. The clastic sediments were ~25% reduced in concentration (with the biogenic sediments similarly increased by ~25%), they were finer–grained, and significantly less rich in ferric iron phases (hematite/goethite). We think these three covarying clastic parameters are due to an interval of reduced clastic flux from the Amazon River Plume with a reduced proportion of Amazon Basin sediments (as opposed to Andes-derived sediments). We hypothesize this was due to significantly drier Amazon Basin environmental conditions during that time interval.

Paleomagnetism of Precambrian dikes in the Kola part of northeastern Fennoscandia and its relation to the Svecofennian orogeny

Based on the results of the preliminary paleomagnetic investigation of 57 Precambrian dikes of the Kola Peninsula, in 31 of them a stable monopolar component of natural remanent magnetization (NRM) is revealed (D = 353.2°, I = 53.0°, K = 58, and α95 = 3.4°). The peculiarities of the distribution of this magnetization component within the Kola Peninsula and the rock magnetic characteristics of the dikes in which this component is isolated suggest its secondary nature and relate the mechanism and formation time to the remagnetization processes which took place in the northwest of Fennoscandia about 1.8 billion years ago during the Svecofennian orogeny. The corresponding geomagnetic pole of Fennoscandia has the coordinates Plat = 54.5°, Plong = 224.0°, and A95 = 3.9° and is located in the immediate vicinity of the known Paleoproterozoic (1.9–1.7 Ga) poles of Baltica (Khramov et al., 1997; Veikkolainen et al., 2014).

Paleomagnetism of the Miocene Jantetelco Granodiorites and Tepexco Volcanic Group and inferences for crustal block rotations in central Mexico — Reevaluation

Miocene igneous rocks from a location in central Mexico provide paleomagnetic data that allow re-evaluation of previous data by Urrutia-Fucugauchi (1981) that were interpreted to suggest a counter clockwise rotation of a crustal block by about 50°. We sampled 31 sites from the Miocene trondhjemitic Chalcatzingo domes, the Tepexco volcanic group, and the Xalostoc diorite, covering the same area of approximately 50km2 about 90km SE of Mexico City. Magnetic analysis shows that these rocks contain magnetic phases of variable composition, with Curie temperatures characteristic for magnetite, but often accompanied by lower Curie temperature components. Magnetic hysteresis measurements point to the presence of PSD particles, and in combination these properties suggest that these rocks are also suitable for paleomagnetic study. Scanning electron microscope analysis supports the rock magnetic results, indicating the presence of magnetite and high-intermediate titanium titanomagnetite in many samples. Demagnetization experiments showed in most cases characteristic remanence directions of reasonable to good quality, and for 26 sites mean directions could be determined. Of these 14 (12) are of normal (reverse) polarity. Overall mean directions of normal and reverse sites are antipodal and pass a reversal test at the 95% probability level. The paleodirection from 26 sites is D=348.1°E, I=35.7°, α95=7.4°, and the paleopole is located at Lat=78.3°N, Long=184.2°E, A95=7.0°, which is indistinguishable from the 20Ma reference pole for the stable North America plate. These data do not support any tectonic deformation of the sampling area since the Miocene. Based on the number of sites studied, their rock magnetic characteristics, and the quality of the magnetic remanence that results in a positive reversal test, we consider our data to be reliable and we therefore suggest that this result supersedes that of Urrutia-Fucugauchi (1981). The reason for this previous and much different result remains unknown.

The use of palaeomagnetism and rock magnetism to understand volcanic processes: introduction

Abstract This Special Publication provides a snapshot of our understanding of volcanic processes through the use of palaeomagnetic and rock magnetic techniques. Here, we provide a context for the book, placing individual chapters within the milieu of previous work, including some magnetic techniques that were not used in the particular studies described herein. Thermoremanent magnetization is a powerful tool to understand processes related to heating and cooling of rocks, including estimating the temperature of emplacement of pyroclastic deposits, which may allow us to better understand the rates of cooling during eruption and transport. Anisotropy of magnetic susceptibility and anisotropy of remanence are used primarily to investigate rock fabrics, and allow the interpretation of flow dynamics in dykes, lava flows and pyroclastic deposits, as well as the location of the eruptive vents. Rock magnetic characteristics can help in the correlation of volcanic deposits but also provide means to date volcanic deposits and to better understand the processes of cooling of the deposits, as the magnetic minerals can change with temperature. In addition, volcanic rocks may be key recorders of past magnetic fields, allowing a better understanding of changes in field intensity and, perhaps, providing clues of how the magnetic field is formed.

About this title ‐ The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes

This volume provides a synopsis of current research on volcanic processes, as gained through the use of palaeomagnetic and rock magnetic techniques. Thermoremanent magnetization information provides a powerful means of deciphering thermal processes in volcanic deposits, including estimating the emplacement temperature of pyroclastic deposits, which allows us to understand better the rates of cooling during eruption and transport. Anisotropy of magnetic susceptibility and anisotropy of remanence are used primarily to investigate rock fabrics and to quantify flow dynamics in dykes, lava flows, and pyroclastic deposits, as well as identify vent locations. Rock-magnetic characteristics allow correlation of volcanic deposits, but also provide means to date volcanic deposits and to understand better their cooling history. Because lava flows are typically good recorders of past magnetic fields, data from them allow understanding of changes in geomagnetic field directions and intensity, providing clues on the origin of Earth's magnetic field.

Paleoenvironmental signature of the Deccan Phase-2 eruptions

The environmental impact of the Deccan trap volcanism is poorly understood as yet. The paucity of geological markers that can unambiguously be attributed to the Deccan volcanism and the temporal coincidence of the volcanism with an asteroid impact make evaluation of volcanic contribution to the end Cretaceous mass extinction difficult. Here we briefly review environmental proxy records of two reference Cretaceous-Tertiary boundary (KTB) sections, Bidart (France) and Gubbio (Italy). In both sections, a change in colour of sediments located just below the KTB is systematically associated with very low values of (low-field) magnetic susceptibility (MS). Rock magnetic characteristics suggest that the decrease in MS values results from the loss (dissolution) of ferrimagnetic mineral in this intervals. In addition to the characteristic change in magnetic assemblage, akaganeite (chlorine-bearing iron oxyhydroxide) is commonly observed under the scanning electron microscope in the low MS intervals at Bidart and Gubbio, but has never been detected in the remaining sedimentary successions. We suggest that the association of granular akaganeite and iron oxides dissolution features can be explained by an ocean acidification and aerosol deposition event linked to the Deccan Phase-2 volcanism.