Formation Of Magnetic Minerals Research Articles

Impact of temperature increase on the formation of magnetic minerals in shales. The example of Tournemire, France

Remagnetization is a pervasive mechanism affecting all kinds of rocks. Sedimentary rocks are particularly prone to such a mechanism because they can experience a wide range of physical and biogeochemical processes which can lead to partial or total loss of the original paleomagnetic record. Temperature increase is one of key factors affecting the rock magnetic properties in sedimentary rocks. Laboratory experiments on shales in the literature have shown that the magnetic mineralogy changed with temperature as low as 50 °C, and that new magnetic phase(s) are formed. The latter was identified to be mostly iron oxides (e.g., magnetite) and iron sulfides (e.g., pyrrhotite). In this study similar to what previously conducted on samples from the Paris Basin, a laboratory heating experiment is conducted on shale samples from the Tournemire tunnel (SE France) in a temperature range of 50 to 130 °C. This aims to simulate a new exposition of the samples to temperature and to identify the changes in magnetic phases, especially on FeIII-bearing minerals, with temperature. The remanence of the analyzed samples increases stepwise, suggesting an increasing concentration of magnetic minerals above their blocking volume with increasing temperature. Magnetite is the main magnetic carrier present and formed in the heated samples, with possibly pyrrhotite forming at high temperature. A conceptual model of magnetic mineralogy changes with temperature is presented and compared to previous results on claystones from the Paris Basin. The experimental observations support that the paleomagnetic record in sedimentary rocks affected by a later temperature increase during burial should be interpreted carefully. Indeed, remagnetization will likely occur when magnetic minerals record a secondary remanence either growing above their blocking volume or when exposed again to a temperature higher than the maximum burial temperature formerly experienced by the samples.

Магнитные свойства стекол, синтезированных на основе горных пород различного генезиса

The structural-phase, chemical composition and magnetic properties of artificial glasses obtained by high-temperature melting of rock mixtures of different genesis: volcanogenic-sedimentary rocks, quartzitic shales, psamite-silt-pelitic complexes were studied. Different in duration cooling and glass transition conditions were used for glass synthesis. The magnetic state of the iron-containing phase and the analysis of the presence and contribution of iron oxides to the magnetic properties were assumed to be the characteristic criterion determining the parameters of the glass formation process. It was shown that the total iron content in artificial glasses depends exclusively on the composition of the initial charge. In this case, the iron-containing component is mainly determined by sedimentary rocks. The formation of magnetic minerals is determined both by the composition of the charge and by the rate of cooling of the melt. During “fast” cooling, the formed magnetic particles are mostly (up to 90% or more of the total content of the magnetic phase in the sample) in a superparamagnetic state. During “slow” cooling, a mixture of particles of different sizes and, accordingly, in different magnetic states is formed: from superparamagnetic to low-domagnetic. The ferrimagnetic phase crystallizing in artificial glasses is represented by chemically heterogeneous aggregates of iron oxides, mainly non-stoichiometric magnetite.

Differential Thermal Analysis Using High Temperature Susceptibility Instruments

Measurements of susceptibility as a function of temperature are an important, standard method of quantifying a sample’s magnetic mineralogy. These measurements are used to identify the Curie/Néel temperatures of constituent minerals and show evidence of thermally-induced oxidation and formation of magnetic minerals. For these reasons, the High Temperature Susceptibility Bridge (HTSB) is a common instrument in paleomagnetism laboratories around the world. Here, we argue that HTSBs can be used to perform simple differential thermal analysis (DTA), a technique used to measure phase transitions and exo-/endothermic reactions by measuring deviations in temperature from a steady heating rate. Because HTSBs are designed to heat samples at a relatively constant rate, the standard susceptibility measurement can be used to obtain similar information, albeit crude, about the phase transitions taking place. For standard samples of vivianite, goethite, and maghemite, we compare the heating curves of the sample and a blank run, to identify DTA-analogous information. In the case of goethite and vivianite, the reactions identified do not have a corresponding expression in susceptibility, demonstrating that this approach expands the utility of this common piece of equipment. We estimate the minimum enthalpy of reactions detectable and their mass dependence. Additionally, we show that this approach is successful in detecting the dehydration of vivianite in a mixed mineralogy natural sample.

Magnetic Structure and its Tectonic Implication Around Longmenshan Fault Zone Revealed by EMAG2v3

The formation of magnetic minerals is bound up with the tectonic evolution history, whereupon the distribution of magnetic anomalies has great meanings for regional tectonics. In this study, we use the latest global lithospheric magnetic field model EMAG2-v3, processed by various techniques including reduction to the pole (RTP), upward continuation, derivations, Euler deconvolution, estimation of total magnetization direction, and Curie point depth (CPD), to unveil the tectonics around Longmenshan fault zone (LFZ). LFZ is clearly displayed as a positive and negative anomaly transition zone in RTP anomalies and acts as a magnetic basement boundary. The Sichuan Basin (SB), located to the east of LFZ, is marked by strong magnetic basement and NE-strike banded induced positive anomalies which are associated with the Neoproterozoic magmatic activity. The banded shape, absence of radial pattern of anomalies, and existence of fossil subduction zone supports that the magnetic basement was formed in arc environment. The CPD in SB estimated by radial average power spectral is 30–51 km, which allows magnetic minerals in deep crust or even in lithospheric mantle to exhibit high magnetizations. The Songpan-Ganzi fold belt (SGFB), in contrast, is located to the west of LFZ and covered by thick and low-susceptibility Triassic deposits of flysch, manifests as weak negative anomalies caused by relatively shallow CPD and widespread remanent magnetization. Significant positive anomalies, appearing around the Manai and Rilonguan granitic massifs, indicate a strong magnetic basement beneath SGFB, which is conjectured as westward extension of the Yangtze Block at depth.

Effect of in-situ combustion process on the magnetic properties and composition of rock

In-situ combustion (ISC) is a proved, effective method for enhanced oil recovery (EOR). In our previous work, we studied the feasibility of ISC process for heavy oil recovery in Nurlat Oil Field (Tatneft oil company, Russia) regarding to oil recovery, in-situ oil upgrading, stability of combustion front, etc. In this work, we investigated the effect of ISC process on the rock properties and composition. We found that magnetic minerals can be in-situ formed in rock during combustion process of oils. The formation of magnetic minerals in rock depends on temperature, heating time, and oil environment. Based on the magnetic properties, the samples can be divided into the most heated, less heated, and nonheated ones with hydrocarbons. The changes in the magnetic properties of rock can be used for developing technologies for combustion front monitoring, which is very valuable for controlling ISC process and its adjustment. Keywords: magnetic properties; thermomagnetic analysis; enhanced oil recovery; in-situ combustion; rock.

Linkages between soil organic matter and magnetic mineral formation in agricultural fields in southeastern Minnesota, USA

Magnetic properties of soil are widely utilized to study soil development in a variety of settings due to the formation of strongly magnetic iron oxides during pedogenesis. Similarly, soil organic matter (SOM) is commonly measured in soil surveys conducted on agricultural lands due to the essential role SOM plays in the soil ecosystem. Here, we present data from two agricultural fields in southeastern Minnesota that demonstrate a relationship between soil magnetic properties and SOM. In each field, we collected 100 topsoil samples along a 40 m by 20 m grid to determine spatial variability in soil magnetic properties and SOM, as well as two soil cores to constrain variability with depth (∼0–60 cm). Magnetic susceptibility, low-field remanence, and hysteresis properties were used to characterize magnetic mineral abundance and grain-size in the soils. There are strong positive correlations between SOM and three magnetic properties: the frequency dependence of susceptibility (χfd), anhysteretic remanent magnetization (ARM), and the ratio of ARM to isothermal remanent magnetization (ARM/IRM). All three of these magnetic properties (χfd, ARM, and ARM/IRM) are sensitive to the concentration (or relative abundance) of fine-grained (<75 nm) magnetite/maghemite known to form in well-drained soils during pedogenesis. Correlation between SOM and magnetic properties persist in each field despite differences in the management strategy over the past three decades. Our results support a functional link between SOM and soil-formed magnetite/maghemite, where increasing SOM (up to a threshold) enhances the production and stability of soil-formed magnetite due to its role in soil redox processes and iron-organic complexes. Agricultural soils seem particularly well suited to demonstrate correlations between SOM and pedogenic magnetic minerals due to their relatively low SOM and typically well-drained environments, supporting the utility of soil magnetism in agricultural soil survey studies.

Temperature dependence of pedogenic magnetic mineral formation in loess deposits

Loess sequences provide some of the most important continental records of climatic change, and various pedogenesis proxies from Chinese loess deposits have provided humidity records for the Miocene through Holocene. Amongst these proxies, magnetic properties have often been used to reconstruct paleoprecipitation; however, an increasing number of studies have recognized that magnetic records from loess deposits are also influenced by temperature and hence they can be used to reconstruct paleotemperatures. In the present study, the magnetic characteristics of modern loessic soils and loessic paleosols from five regions spanning a broad climatic gradient were studied to investigate the temperature dependence of the pedogenic production of magnetic minerals. The results indicate that the magnetic characteristics are dependent on the temperature of particularly season, rather than mean annual temperature in temperate region. The findings can potentially provide insights into changes in climatic seasonality on geological timescales.

Remagnetized limestones and dolostones from the Upper Cambrian La Flecha Formation, La Rioja province, Argentine Precordillera

Representative rock-magnetic experiments and petrographic studies on remagnetized limestones and dolostones from the Upper Cambrian La Flecha Formation (Quebrada La Angostura, Precordillera of La Rioja, Argentina) carrying a pre-tectonic Permo-Triassic secondary magnetization are reported in order to improve the understanding of the pervasive Sanrafaelic overprint that reset the palaeomagnetic record of most of the Early Cambrian to Mid-Ordovician units of the Argentine Precordillera and the San Rafael Block. The main carrier of the remagnetization is determined as fine-grained magnetite of chemical origin, though three additional ferromagnetic phases were identified (pyrrhotite, hematite and goethite). A power-law model fitted to hysteresis ratio data (Mrs/Msvs. Bcr/Bc) defined an almost identical trend as that of the limestones from the Middle-Ordovician Ponón Trehué Formation (San Rafael Block, Mendoza province, Argentina) which were affected by the same regional event. Magnetic fabrics revealed by anisotropy of magnetic susceptibility and of anhysteretic remanence show mostly a pre-tectonic origin and, in some cases, a secondary overprint probably related to recent formation of magnetic minerals.

Magnetic method applying for the control of productive land degradation

The development of agriculture in Ukraine requires increasing of the crop yields, which can lead to soil and humus loss, soil erosion and land degradation. The task of soil mapping and modeling within the farm lands is important to predict and control hazard processes in soil. The expected result is the elaboration of the optimal schemes of land exploitation and sustainable use management. To solve these tasks we propose to involve magnetic methods of the soil studies. They give us highly informative techniques based on our own and international experience. The first case of our investigation is magnetic susceptibility of agricultural land within Kharkiv region. The soil is presented by chernozems. We registered the average value of the soil mass-specific magnetic susceptibility (χ): 69×10 –8 m 3 /kg; minimum value is 50×10 –8 m 3 /kg; maximum value is 86×10 –8 m 3 /kg. The coefficient of variation is 12.48 %, which indicates the low variability of magnetic susceptibility within the area. This indicate the absence of the soil type change and technogenic impact. The second example was conducted within the Odessa region. The landscape represents the plain with the bluff near the sea lanes. Lateral cross-section was investigated to identify the parts with the high level of soil erosion dangerous. The magnetic susceptibility of highly magnetic not disturbed southern chernozems reached 160×10 –8 m 3 /kg. We identified the points of the replacement of top soil. This eroded soil, which was presented by underlying clay horizon, has the magnetic susceptibility about 80×10 –8 m 3 /kg. Humus content in soil is closely connected with the formation of magnetic minerals in the soil under the pedogenic process. We mean in this case the absence of the anthropogenic and technogenic impact. The formation of magnetic minerals is controlled only by the presence of organic matter in soil aggregates and favorable conditions for the iron valence change. The productive Ukraine top soil contains fine-grained oxidized magnetite and maghemite of pedogenic origin formed by weathering of the parent material. This soil is often presented by chernozems from the farm lands with the high level of erosion risk. The formation of the magnetite is related to the magnetotactic bacteria functions.

Formation of magnetic minerals at hydrocarbon-generation conditions

In this paper, we report the pyrolysis and formation of magnetic minerals in three source rock samples from the Wessex Basin in Dorset, southern England. The experimental conditions in the laboratory recreated the catagenesis environment of oil source rocks. Magnetic analysis of both the heated and the unheated samples at room temperature and at very low-temperatures (5 K), coupled with transmission electron-microscopy imaging and X-ray analysis, revealed the formation of nanometre-sized (<10 nm), magnetic particles that varied across the rock samples analysed, but more importantly across the pyrolysis temperature range. Magnetic measurements demonstrated the formation of these magnetic minerals peaked at 250 °C for all rock samples and then decreased at 300 °C before rising again at 320 °C. The newly formed magnetic minerals are suggested to be primarily pyrrhotite, though magnetite and greigite are also thought to be present. The sizes of the magnetic minerals formed suggest a propensity to migrate together with oil potentially explaining the magnetic anomalies observed above and within oil fields.

High-resolution magnetic susceptibility measurements for investigating magnetic mineral formation during microbial mediated iron reduction

Disimilatory iron-reducing bacteria play an important role in the reduction of Fe(hydr)oxides and the production of secondary solid-iron mineral phases that can have magnetic properties. Magnetic susceptibility can therefore play an important role in identifying zones where microbial-mediated iron reduction is occurring. We investigated the magnetic susceptibility variations in a hydrocarbon-contaminated aquifer where methanogenesis and iron reduction are the main biogeochemical processes. Our objectives are to (1) determine the variability of magnetic susceptibility, (2) determine the hydrobiogeochemical controls on the magnetic susceptibility variability, and (3) evaluate the use of magnetic susceptibility as a viable technique for identifying zones where the coupling of iron and organic carbon cycling is occurring. Magnetic susceptibility data were acquired down 11 boreholes within contaminated and uncontaminated locations. We show that magnetic susceptibility values for boreholes within the free phase plume are higher than values for boreholes within the dissolved phase plume and background. Magnetic susceptibility values are highest within the zone of water table fluctuation with peaks predominantly occurring at the highest water table marks and are also coincident with high concentrations of dissolved Fe(II) and organic carbon content, suggesting that the zone of water table fluctuation is most biologically active. High magnetic susceptibility values within the vadose zone above the free phase plume are coincident with a zone of methane depletion suggesting aerobic or anaerobic oxidation of methane coupled to iron reduction. Our results suggest that magnetic susceptibility can be used as a viable tool in iron and carbon cycling studies.

A new oil-window indicator? The magnetic assemblage of claystones from the Baffin Bay volcanic margin (Greenland)

Identifying independent parameters to bracket the oil window in sedimentary basins is of first importance for petroleum exploration. We investigate the magnetic assemblage of Cretaceous claystones collected from the western volcanic margin of Greenland. These claystones experienced low-grade burial ( 300 K) properties of isothermal remanent magnetization. The magnetic assemblage of immature claystones (lower Ro) resides in goethite, greigite, and some magnetite. The magnetic assemblage of immature to early mature claystones (higher Ro) resides in stoichiometric magnetite and fine-grained pyrrhotite. By comparing these results with those from claystones from the Paris Basin (France) and the Jura Mountains (Switzerland), we suggest the existence of similar mechanisms for the formation of magnetic minerals during burial. If confirmed by further studies, the magnetic assemblage of claystones may be diagnostic of oil windows.

Burial, claystones remagnetization and some consequences for magnetostratigraphy

AbstractWe investigate the broad lines of magnetic mineral formation for non-metamorphic claystones. More particularly, we focus on the formation of magnetite from c. 20 day-experiments aiming to reproduce burial conditions. It is shown that the sole action of temperature from 50 °C to 250 °C leads to the formation of magnetite. The neoformed magnetites carry a chemical remanent magnetization which equates at least the natural remanent magnetization. We propose a schematic of burial with three magnetic windows where a chemical remanent magnetization superimposed the natural remanent magnetization. These are the greigite window (subsurface), the magnetite window (depth &gt; 2 km) and the pyrrhotite window (depth &gt; 6 km). The formation of magnetic minerals has profound consequences for the magnetostratigraphy record. We propose a conceptual model that shows that the continuous production of magnetite during burial may result in magnetozones that have no relation to the age of the sediment.

Iron reduction and magnetite biomineralization mediated by a deep-sea iron-reducing bacteriumShewanella piezotoleransWP3

[1] Dissimilatory iron reduction (DIR) plays an important role in element biogeochemical cycling. However, little is known about DIR processes and the mineralization abilities of strains found in deep oceans, where ecology, nutrient availability, and diversity are significantly different. Shewanella piezotoleransWP3 is a psychrotolerant and piezotolerant iron-reducing strain with a complex respiration net which has been recently isolated from West Pacific deep-sea sediments at a water depth of ∼1914 m. In this study, we have investigated the biomineralization process ofS. piezotoleransWP3 at 0.1 MPa (∼1 atmospheric pressure) and 20°C (optimum growth temperature). A series of magnetic measurements in combination with X-ray diffraction, transmission electron microscopy, and chemical methods were applied to characterize the iron reduction process and biominerals. The results demonstrate thatS. piezotoleransWP3 can reduce hydrous ferric oxide (HFO) at a much faster rate than that of most other reported strains and produce superparamagnetic magnetite particles with an average grain size of 4–6 nm after 72 h. Time course multiple magnetic parameters can be used to effectively monitor the transformation process from weak antiferromagnetic HFO to strong ferrimagnetic magnetite. Changes in concentration-sensitive and grain size–sensitive magnetic parameters suggest that the biomineralization process is characterized by recurring magnetic mineral formation and particle growth. Owing to its high iron reduction rate,S. piezotoleransWP3 may contribute to iron mineral transformation and element cycling in deep oceans. Our results additionally suggest that the multiple-parameter rock-magnetic method is a fast, sensitive, nondestructive and quantitative approach for monitoring DIR biomineralization processes involving magnetic minerals.

The magnetic properties of loess and paleosol samples from the Chinese Loess Plateau spanning the last 22 million years

Magnetic measurements (susceptibility, isothermal and anhysteretic remanence, and quotients derived from these) are presented for a suite of loess and paleosol samples from sites on the Chinese Loess Plateau. The three sites, Xifeng, Dongwan and Qinan (QA-I), together span most of the last 22 million years. The results provide the first multi-parameter magnetic measurements from pre-Pleistocene loess/paleosol sequences that began accumulation in the early Miocene. Mass specific measurements have been corrected for carbonate concentrations which peak in the loess layers and range up to 57%. All the magnetic properties recorded indicate variability on both orbital and supra-orbital timescales. The changing magnetic properties allow the record to be divided into a sequence of eight sample groups that broadly parallel the main supra-orbital changes in magnetic susceptibility. The pre-Pleistocene parts of the record include intervals (mainly late Miocene and Pliocene) during which loess as well as paleosol layers are characterized by high values for properties such as frequency dependent susceptibility ( χ fd), usually associated with strong weathering. Most of the Miocene record prior to 8.5 Ma, with the exception of a brief interval from ca. 14.4 to 15.9 Ma, shows reduced values for indicators of pedogenic ferrimagnetic concentrations in both the loess and paleosol layers, as well as a low amplitude of variability between loess and paleosol values. The palaeoenvironmental implications of this part of the sequence are unclear since they hinge on the type of model of pedogenic magnetic mineral formation adopted. High-field remanence measurements indicate that the coercivity of the antiferromagnetic minerals represented declined progressively throughout the whole period in both the loess and the paleosol samples, though there is no unambiguous evidence for long-term diagenetic alteration of the magnetic properties on timescales beyond the orbital ones that drive the loess/paleosol alternations. The present results suggest caution in applying existing climofunctions based on magnetic susceptibility to deposits spanning the whole of the last 22 Ma.

Nondestructive continuous physical property measurements of core samples recovered from hole B, Taiwan Chelungpu‐Fault Drilling Project

The Taiwan Chelungpu‐Fault Drilling Project was undertaken in 2002 to investigate the faulting mechanism of the 1999 Mw 7.6 Taiwan Chi‐Chi earthquake. Hole B penetrated the Chelungpu fault, and core samples were recovered from between 948.42‐ and 1352.60‐m depth. Three major zones, designated FZB1136 (fault zone at 1136‐m depth in hole B), FZB1194, and FZB1243, were recognized in the core samples as active fault zones within the Chelungpu fault. Nondestructive continuous physical property measurements, conducted on all core samples, revealed that the three major fault zones were characterized by low gamma ray attenuation (GRA) densities and high magnetic susceptibilities. Extensive fracturing and cracks within the fault zones and/or loss of atoms with high atomic number, but not a measurement artifact, might have caused the low GRA densities, whereas the high magnetic susceptibility values might have resulted from the formation of magnetic minerals from paramagnetic minerals by frictional heating. Minor fault zones were characterized by low GRA densities and no change in magnetic susceptibility, and the latter may indicate that these minor zones experienced relatively low frictional heating. Magnetic susceptibility in a fault zone may be key to the determination that frictional heating occurred during an earthquake on the fault.

Crustal magnetization of Mars controlled by lithology or cooling rate in a reversing dynamo?

To explain the lack of magnetization in large portions of the Noachian crust, a lithological origin has been put forward, corresponding to the lack of formation of magnetic minerals in the crustal rocks. An alternative hypothesis is proposed here, with constant amount of magnetic minerals, but variable reduction of total magnetization over the magnetic thickness, due to variable record of successive polarities of the magnetizing field. Large crustal cooling rates would correspond to strongly magnetized zone, and slow cooling rates to poorly magnetized zone. Based on this model we derive an explanation for the proposed confinement of magnetized zones within the inter‐tropical band.

Record of Late Pleistocene Glaciation and Deglaciation in the Southern Cascade Range. II. Flux of Glacial Flour in a Sediment Core from Upper Klamath Lake, Oregon

During the late Wisconsin, glacial flour from alpine glaciers along the east side of the Cascade Range in southern Oregon was deposited in Upper Klamath Lake. Quantitative interpretation of magnetic properties and grain-size data of cored sediments from Caledonia Marsh on the west side of the lake provides a continuous record of the flux of glacial flour spanning the last ≈37 000 calendar years. For modeling purposes, the lake sediments from the 13-m core were divided into three sedimentary components defined from magnetic, geochemical, petrographic, and grain-size data. The components are (1) strongly magnetic, glacial flour made up of extremely fine-grained, fresh volcanic rock particles, (2) less magnetic lithic material made up of coarser, weathered volcanic detritus, and (3) non-magnetic biogenic material (largely biogenic silica). Quantitative interpretation is possible because there has been no significant postdepositional destruction or formation of magnetic minerals, nor alteration affecting grain-size distributions. Major steps involved in the interpretation include: (1) computation of biogenic and lithic components; (2) determination of magnetic properties and grain-size distributions of the non-glacial and glacial flour end-members; (3) computation of the contents of weathered and glacial flour components for each sample; (4) development of an age model based on the mass accumulation of the non-glacial lithic component; and (5) use of the age model and glacial flour contents to compute the flux of glacial flour. Comparison of the glacial flour record from Upper Klamath Lake to mapped glacial features suggests a nearly linear relation between flux of glacial flour and the extent of nearby glaciers. At ≈22 ka, following an extended period during which glaciers of limited size waxed and waned, late Wisconsin (Waban) glaciers began to grow, reaching their maximum extent at ≈19 ka. Glaciers remained near their maximum extent for ≈1000 years. During this period, lake sediments were made up of ≈80% glacial flour. The content of glacial flour decreased as the glaciers receded, and reached undetectable levels by 14 ka.

The Application of Iodine and Magnetic Susceptibility Surface Geochemical Surveys in the Lodgepole Play, Eastern Williston Basin, North Dakota: ABSTRACT

Summary The use of surface geochemistry as a first pass exploration tool is becoming more prevalent in petroleum exploration. This is especially true due to the high cost of 2-D and 3-D seismic surveys in defining small targets such as the Waulsortion mounds of the Lodgepole Formation. Surface geochemical surveys are very effective in pinpointing specific target areas for seismic surveying and thus reducing costs. The type of survey varies from a reconnaissance type to a detail survey that focuses on specific areas for seismic exploration. Presented here are iodine and magnetic susceptibility surveys that can be used to define Heath. Mission Canyon. Lodgepole and Red River reservoirs. These type of surveys are very effective in minimizing the cost of seismic surveying and maximizing exploration effort. When the purpose of a surface geochemical survey is clearly define, properly planned and implementation is successful, the results can lead to a significant increase in new field discoveries and a decrease in the number of dry holes. Characteristically, surface geochemical surveys, when properly carried out. have been 100% accurate on predicting dry boles and when integrated with seismic have caused success rates to exceed 50% success rate over rank wildcats. Surface Geochemistry The use of iodine surface geochemistry and the current theories of vertical migration are presented in Tedesco (1994). The specific method presented in this paper is the analysis of iodine in magnetic susceptibility of soil Hydrocarbons migrating to the surface bond with iodine at the soil air interface under the influence of sunlight. Because of the stability of iodorganic compounds, iodine at the surface can be used as an exploration tool.The iodine analysis used in this survey is the most recent method and has a detection range of .004 to 20+ ppm iodine. The type of anomalous patterns for any surface geochemical methods has been termed as both halo (surrounding the reservoir) or apical (overlying the reservoir). Both types exist and most anomalies are combinations of hale and apical anomalies. Magnetic susceptibility measurements are based an the concept that migrating hydrocarbons cause the formation of magnetic minerals in the soil. The presence of these magnetic minerals are detected by changes in the magnetic signature of the soil.

The Upper Kaena sedimentary geomagnetic reversal record from southern Sicily

A detailed paleomagnetic and rock magnetic record of the upper Kaena polarity reversal was determined from late Pliocene marine marls in southern Sicily. Two separate characteristic magnetization components were distinguished: a low‐temperature (LT) component between 200° and 50°C and a high‐temperature (HT) component between 500° and 580°–610°C. The two components record the reversal in a slightly different way, but both were acquired in an early stage following deposition, most probably by authigenic (biogenic) formation of magnetic minerals. The actual (R‐N) reversal, via E and horizontal inclinations, seems to take 3.3 kyr and is followed by a stable normal interval (3.3 kyr) and subsequently by a significant excursion (50°–60°) in declination (3.6 kyr). Relative intensities were lower during a time‐span of 5.6 kyr and show a minimum of 10% of the nontransitional values, but during the excursion, no intensity changes are apparent. The VGPs of the HT component are confined to a longitude between India and Australia; those of the LT component oscillate between this same longitude and one passing over North and South America. We conclude that most if riot all observed features are largely determined by the remanence acquisition process which is complicated by authigenic formation of magnetic minerals and cyclically fluctuating paleoredox conditions. This has not only resulted in considerable smoothing but also in delayed NRM acquisition in specific sedimentary intervals. We believe that the observed “excursion” is a sedimentary artifact and not related to geomagnetic field behavior during transitions. We emphasize that many reported “geomagnetic” features may in fact be due to the sedimentary remanence acquisition process.