Palaeomagnetic Study on the Precambrian-Cambrian Boundary Candidate Stratotype Section at Meishucun, Yunnan

The Meishucun secton has been recommended as an international candidate stratotype secton of thePrecambrian-Cambrian boundary. The paper deals with the palaeomagnetic study on the section. A total of159 palaeomagnetic samples were successively collected from the platform-facies sequence of carbonates andphosphates at the section. Thermal demagnetization results indicate a great majority of the rocks at the sectionhave been strongly overprinted by recent magnetic field, but 57 samples have preserved remanentmagnetization with antipodal directions (mean D/I=4.2°/ 7.1°, K=9, α_(95) = 6.6°). Baaed on calculation,the location of the palaeomagnetic pole was at 68.8°N and 270.7°E, which is different from any palaeopolesobtained from younger Phanerozoic rocks in South China. The results reveal a polarity zonation which in-cludes at least 9 reversal events. A comparison of China's magnetostratigraphic records with those fromSiberia, Australia and the western U.S.A. shows that all the sections are characterized by frequent polarity re-versals.     

Palaeomagnetic data from the precambrian Gwalior traps, Central India

From alternating-field and thermal demagnetization studies on two dolerite “Traps” in the Gwalior Series (Central India), dated at 1830 ±200 m.y., three different palaeomagnetic directions could be distinguished. The characteristic magnetization component, which is considered as the primary magnetization, has a mean direction: D=78°, I=+34.5°, α₉₅=5°, k=369, N=4 (Pole): 155.5°E19°N, dp=3°, dm=5.5°.A comparison of the presented data with other Precambrian and Phanerozoic data from the Indian subcontinent might suggest that the Indian subcontinent underwent a continuous anticlockwise rotational movement during the last 1800 m.y.     

Palaeomagnetic evidence for Tertiary counterclockwise rotation of Adria

With the aim of obtaining Tertiary palaeomagnetic directions for the Adriatic Foreland of the Dinaric nappe system, we carried out a palaeomagnetic study on platform carbonates from stable Istria, from the northwestern and the Central Dalmatia segment of imbricated Adria. Despite the weak to very weak natural remanences of these rocks, we obtained tectonically useful palaeomagnetic directions for 25 sites from 20 localities. All exhibit westerly declinations, both before and after tilt correction. Concerning the age of the magnetizations, we conclude that five subhorizontal and magnetite bearing Eocene localities from stable Istria are likely to carry primary remanence, whereas three tilted and hematite-bearing ones were remagnetized. In the northwestern segment of imbricated Adria the cluster of the mean directions improved after tectonic correction indicating pre-tilting magnetization. In contrast, Maastrichtian–Eocene platform carbonates from Central Dalmatian were remagnetized in connection with the late Eocene–Oligocene deformation or Miocene hydrocarbon migration. Based on the appropriate site/locality means, we calculate mean palaeomagnetic directions for the above three areas and suggest an alternative interpretation of the data of Kissel et al. [J. Geophys. Res. 100 (1995) 14999] for the flysch of Central Dalmatia. The four area mean direction define a regional palaeomagnetic direction of Dec=336°, Inc=+52°, k=107, α₉₅=9°. From these data we conclude that stable Istria, in close coordination with imbricated Adria, must have rotated by 30° counterclockwise in the Tertiary, relative to Africa and stable Europe. We suggest that the latest Miocene–early Pliocene counterclockwise rotations observed in northwestern Croatia and northeastern Slovenia were driven by that of the Adriatic Foreland, i.e. the rotation of the latter took place between 6 and 4 Ma.     

Multicomponent magnetization in western Dolpo (Tethyan Himalaya, Nepal): tectonic implications

A palaeomagnetic study has been carried out in the Tethyan Himalaya (TH; the northern margin of Greater India). Twenty-six palaeomagnetic sites have been sampled in Triassic low-grade metasediments of western Dolpo. Two remanent components have been identified. A pyrrhotite component, characterized by unblocking temperatures of 270–335 °C, yields an in situ mean direction of D=191.7°, I=−30.9° (k=29.5, α₉₅=5.7°, N=23 sites). The component fails the fold test at the 99% confidence level (k_{in situ}/k_bed=6.9) and is therefore of postfolding origin. For reason of the low metamorphic grade, this pyrrhotite magnetization is believed to be of thermo-chemical origin. Geochronological data and inclination matching indicate an acquisition age around 35 Ma. The second remanence component has higher unblocking temperatures (>400 °C and up to 500–580 °C range) and resides in magnetite. A positive fold test and comparison with expected Triassic palaeomagnetic directions suggest a primary origin.The postfolding character of the pyrrhotite component, and its interpreted age of remanence acquisition, implies that the main Himalayan folding is older than 35 Ma in the western Dolpo area. This study also suggests that the second metamorphic event (Neo-Himalayan) was more significant in the Dolpo area than the first (Eo-Himalayan) one.A clockwise rotation of 10–15° is inferred from the pyrrhotite component, which is compatible with oroclinal bending and/or rotational underthrusting models. This rotation is also supported by the magnetite component, indicating that no rotation of the Tethyan Himalaya relative to India took place before 35 Ma.     

Palaeomagnetic study of the Nagssugtoqidian mobile belt in Central-West Greenland

This paper reports a palaeomagnetic study of amphibolite and granulite facies basement rocks across a 60 km wide north-south traverse through the Nagssugtoqidian mobile belt in West Greenland, which incorporates the c. 2500 Ma Itivdleq shear belt, the c. 1800 Ma Ikertôq shear belt, and adjoining terrains. It also integrates the results with earlier investigations of the belt to produce a composite record of the magnetic field during uplift and cooling of the terrain through c. 600–500°C at c. 1750–1600 Ma. Progressive a.f. and thermal cleaning of samples from 81 sites identifies a range of magnetic components. Lowest blocking temperature remanences in Nagssugtoqidian (c. 1700 Ma) amphibolite facies rocks yield steep W to N positive components residing in magnetite. Granulite facies rocks formed at c. 1800 Ma generally have a dual record incorporating steep N to NW positive components unblocked by 580°C and shallow E-W directed components of dual polarity only unblocked close to the Curie point of haematite. A common feature of relict c. 2500 Ma amphibolite and granulite facies terrains is a progressive movement of sample directions back along a palaeofield migration path with treatment and is interpreted to represent the recovery of a discrete spectrum acquired during a.p.w. Areas with a distributed spectra through the critical range of blocking temperatures, altitude-controlled sections, and blocking temperature relationships all record consistent a.p.w. during the interval of uplift-related cooling. The collective data define a clockwise palaeofield migration path between D = 174, I = 32°, and D = 348, I = 66° referred to as the ‘A’ magnetisation. The equivalent palaeopoles define one limb of an a.p.w. loop conforming to other Laurentian poles assigned to the interval 1750–1650 Ma and widely represented as a post-Hudsonian overprinting or cooling remanence. Shallow E-W directions, designated ‘B’, predominate in late tectonic diorites and are therefore younger than 1700 Ma; they appear to represent a localised reheating event near the northern margin of the Ikertôq shear belt, possibly related to this magmatism, which produced the hemoilmenite phases. The equivalent palaeopoles are provisionally interpreted to represent part of the return path of the APW loop because they are coincident with other poles dated c. 1630 Ma. Collectively the palaeofield migration data from all studies define a thermal dome broadly coincident with the Ikertôq shear belt, but it is not possible to isolate the contribution of components of vertical movement along faults running through the belt to this regional effect.     

The Hilina Pali palaeomagnetic excursion and possible self‐reversal in the loess from western Ukraine

A loess‐palaeosol succession from the last glacial cycle was palaeomagnetically studied in the Rivne abandoned brickyard (western Ukraine). Two samples of undisturbed loess from the same depth of parallel sections display steep negative inclinations. These reversed directions in the loess dated at c. 18 ka may possibly be correlated with the Hilina Pali palaeomagnetic excursion. This is the first occurrence of the Hilina Pali in a loess sediment. Unfortunately, the loess with negative inclination does not form any continuous layer that could be suitable for studies of detailed features of geomagnetic field inversion. Another six samples from an illuvial horizon of the Holocene soil also showed negative inclinations and strongly deviated declinations. This part of the section does not represent, however, any palaeomagnetic excursion. The anomalous magnetization in maghemite‐ and titanomagnetite‐rich sediment results most probably from self‐reversal remagnetization. A new insight into palaeomagnetic excursions noted in loess, especially in its parts affected by pedogenic processes, is recommended.     

Palaeomagnetic and potassium‐argon dating studies of the Tasmanian Dolerites

The stable magnetizations of the Tasmanian Dolerites are shown to fall into two distinct groups depending upon their directions and the geographical region of the dolerites. It has been suggested that this could be a result of significant age differences between the dolerites of these groups. A series of K‐Ar determinations indicates that there is no detectable systematic age differences and the average of the five bodies dated is 170.5 ± 8.0 m.y. (not significantly different from previous K‐Ar dates from a single body). A re‐appraisal of the palaeomagnetic data, in the light of the distinct groupings of the directions, yields two significantly different pole positions‐ Lat 50.7°S, Long. 174.5°E (A_9r, = 5.2°) and Lat. 47.7 °S, Long. 123.5° (A₉₅ = 9.5°)’. The former of these is in excellent agreement with pole positions from other Lower to Middle Jurassic rocks of Australia but the significance of the latter remains obscure.     

Palaeomagnetic reconnaissance result from the maubisse formation,east timorand its tectonic implication

A preliminary palaeomagnetic investigation of the supposedly allochthonous Permian Maubisse Formation in East Timor yielded a mean direction of magnetization of decl. = 140E, incl. = +45 and α₉₅ = 13°. This direction is indistinguishable from that of the autochthonous Permian Cribas Formation reported earlier. The apparent agreement between the palaec magnetism of the two Formations is interpreted to imply that both are autochthonous and have been part of the Australian continental margin since the Permianand does not support the supposed Asian origin for the Maubisse Formation.     

Magnetostratigraphy and lithostratigraphy of the Laño vertebrate-site: Implications in the uppermost Cretaceous chronostratigraphy of the Basque-Cantabrian Region

Here we present the magnetostratigraphic dating of the Laño locality (Condado de Treviño, northern Iberian Peninsula), one of the most noteworthy Campanian-Maastrichtian vertebrate sites of Europe. A composite section of 75 m thickness (Laño quarry) constructed from multiple, overlapping profiles and a continuous one (Faido) have been sampled for magnetostratigraphy. Thermal demagnetization techniques were systematically applied to 161 standard specimens and allowed characterizing the characteristic remanent magnetism, mostly carried out by magnetite. The palaeomagnetic signal is slightly scattered due to variety of lithologies, but the primary character can be guaranteed, since the normal and reverse directions are pseudo antiparallel; 346, 28 (α₉₅: 11.9°, k: 5.3) and 175, −35 (α₉₅: 16.4°, k: 4.6). Reliable samples allowed us to build the local polarity sequence made of eight magnetozones that has been used to correlate to the Global Polarity Time Scale. The age of the lower part of the Laño-village succession is basal late Campanian (Hoplitoplacenticeras marroti ammonite zone) and fits with the long reversed zone that must correlate to Chron C33r. The pattern of magnetozones allows tracking the section up to C30r at the upper part of the profile. In this correlation, the Laño vertebrate site is regarded as latest Campanian in age as it falls within the C32n (≈72–73.5 Ma). The combined lithostratigraphic and magnetostratigraphic analyses have yielded additional conclusions regarding the vertebrate assemblages that are representative of the Late Campanian of the Iberian Peninsula, in addition to highlight an older occurrence in Europe of some vertebrate groups such as salamandrid lissamphians and anguid lizards (or amphisbaenians).     

Palaeomagnetism and magnetostratigraphy of the Permian–Triassic northwest central Siberian Trap Basalts

A detailed palaeomagnetic and magnetostratigraphic study of the Permian–Triassic Siberian Trap Basalts (STB) in the Noril'sk and Abagalakh regions in northwest Central Siberia is presented. Thermal (TH) and alternating field (AF) demagnetisation techniques have been used and yielded characteristic magnetisation directions. The natural remanent magnetisation of both surface and subsurface samples is characterised by a single component in most cases. Occasionally, a viscous overprint can be identified which is easily removed by TH or AF demagnetisation.The resulting average mean direction after tectonic correction for the 95 flows sampled in outcrops is D=93.7°, I=74.7° with k=19 and α₉₅=3.3°. The corresponding pole position is 56.2°N, 146.0°E.Unoriented samples from four boreholes cores in the same regions have also been studied. They confirm the reversed–normal succession found in outcrops. The fact that only one reversal of the Earth's magnetic field has been recorded in the traps can be taken as evidence for a rather short time span for the major eruptive episode in this region. However, there is evidence elsewhere that the whole volcanic activity associated with the emplacement of the STB was much longer and lasted several million years.     

Palaeomagnetism and chronology of Caledonian igneous episodes in the Cross Fell Inlier and northern Lake District

This study employs palaeomagnetism to differentiate between Palaeozoic minor intrusions in northern England. The lamprophyres of the Cross Fell Inlier subdivide petrographically into kersantites and minettes. All the kersantites have steep directions of magnetisation probably correlating with an interval of anomalous geomagnetic field in Caradocian times. The Threlkeld–St John's microgranodiorite (445 m.y.) and Carrock Fell dolerite dyke swarm also possess steep magnetisations assigned to the same interval. The minettes have shallow directions of magnetisation similar to the Shap Granite (393 m.y.) and correlate with the later Caledonian intrusions of northern England. These episodes of intrusion are separated by late-Silurian tectonism and define a trend of increasing K₂O/Na₂O in the later magmas of the Caledonian orogeny. Miscellaneous palaeomagnetic results from the Borrowdale Volcanic Group, Embleton diorites and Haweswater dolerite are also reported.     

New Precambrian palaeomagnetic constraints on the position of the North China Block in Rodinia

We report new palaeomagnetic results from a ca. 1300 to 800 Ma continental shelf succession on the southern margin of the North China Block. A total of 386 oriented core samples were subjected to stepwise demagnetisation. Two overprint components (‘A’ and ‘B’) were identified, with ‘A’ being a Recent geomagnetic field component and ‘B’ a likely Mesozoic remagnetisation related to collision of the North and South China Blocks. An interpreted primary remanence was isolated from six rock units. The most reliable results are as follow, in the order of stratigraphic ascendance. (1) Purple mudstone, muddy sandstone and andesite of the lower Yunmenshan Formation (Rb–Sr age ca. 1270 Ma) yields a high-temperature component that passes both reversal and fold tests and gives a palaeopole at (60.6°S, 87.0°E, A₉₅ = 3.7°). (2) Mudstone in the overlying Baicaoping Formation yields a high-temperature component with a palaeopole at (43.0°S, 143.8°E, A₉₅ = 11.1°). (3) Purple sandstone of the earliest Neoproterozoic Cuizhuang and Sanjiaotang Formations exhibits a high-temperature component that provides a palaeopole at (41.0°S, 44.8°E, A₉₅ = 11.3°). Based on both our new results and a critical selection of available palaeomagnetic data, we construct a preliminary apparent polar wander path (APWP) for the North China Block between 1300 and 510 Ma. Regardless of alternative polarity options applicable to these poles, North China was located within equatorial latitudes for much of this interval. Comparing the North China poles with coeval poles from Laurentia suggests that the two continents were situated on the same plate between 1200 and 700 Ma. North China was thus likely part of the supercontinent Rodinia. Separation of North China and Laurentia occurred between 650 and 615 Ma.     

The West European stress field: new data and interpretation

The mapped stress field of Western Europe reflects the tectonic process active there. A traverse of stress measurements from the Alps and through their northern foreland to the southern border of the Lower Rhine Embayment identifies three distinct stress sub-provinces; the Western Alps, the blocks on both flanks of the Rhinegraben, and the Rhenish Shield. The Alps have high magnitude stresses up to 35 MPa in the direction of maximum compression, here called δ_1h. The general direction of δ_1h is about 140°. The foreland has the same directional trend of δ_1h with a magnitude reduced to about 2.0 MPa. Local anomalies in magnitude and direction occur along the course of the Rhinegraben which is a site of active sinistral shear. The Rhenish Shield shows an internal zonation of the stress field. The magnitudes of the stresses are low (usually negative) along the axis connecting the northern end of the Rhinegraben with the rifting of the Lower Rhine Embayment. The direction there is about 150°. On the eastern and western flanks of the shield the stress directions are essentially the same as in the southern blocks. These zones are distant from the belt of active strain release, consequently stresses of up to 4.0 MPa have accumulated.     

Cretaceous palaeomagnetic results from Hainan Island in south China supporting the extrusion model of Southeast Asia

We report the Cretaceous palaeomagnetic results from Hainan Island, south China. In Hainan island we collected the Early Cretaceous redbeds of the Lumuwan Formation at eleven sites. We also describe the tectonic kinematics for and around Hainan Island since the Cretaceous, deduced from our and previous palaeomagnetic results. The palaeolatitude of Hainan Island is 25.9°N (+3.4°/−3.2°), implying that Hainan island was situated about 7° north from the present position during the Cretaceous. The palaeopole of Hainan Island (latitude = 77.7°N, longitude = 162.1°E, k=65.6, and A₉₅=4.4°) suggests 4.0±5.8° counterclockwise rotation and 14.1±5.5° southward translation relative to the suspected coherent part of the south China block (SCB) since the Cretaceous. The rotation and translation of similar sense (18.8±7.4° and 7.8±6.9°, respectively) are detected in the existing palaeomagnetic result from the Xinlong Formation in Guangxi, which is situated approximately 400 km north-northwest from Hainan Island. The southward translation of both areas seems to have been due to the southeastward extrusion of dissected zones within the southwestern part of the SCB in a similar pattern to the Indochina block, which had resulted from the indentation of India into Asia. This SW part seems to have slightly rotated counterclockwise, because its extrusion was probably smaller in scale than the Indochina block and therefore it was dragged out by the Indochina block. This hypothesis is supported by the existence of a northwest–southeast-trending fault system parallel to the Red River Fault.     

An EXAFS study of Gd,Er and Lu site location in the epidote structure

L _III edge extended X-ray absorption fine structure (EXAFS) spectra of Gd, Er and Lu environments in synthetic epidotes of composition CaLa_0.9 X _0.1Al₂MgSi₃O₁₃H (X=Gd or Er or Lu) were recorded using synchrotron radiation. The Fourier transforms of the Gd-, Er- and Lu-EXAFS are clearly different from one another indicating wholly or partially different site occupancy. Model fitting of the Fourier-filtered partial EXAFS and comparison of pair distribution functions with those calculated for natural epidote leads to the conclusion that three different sites are probably involved in the accommodation of these elements in the epidote structure, and that site preference is a function of the rare earth ionic size. Gd is located in A2-type sites, whereas the local atomic environment of Er is consistent with A1 site occupancy and the Lu environment has been modelled on an M3-type octahedral site.     

Palaeomagnetism and tectonic rotation of the Hastings Terrane,eastern Australia

The Hastings Terrane comprises two or three major fragments of the arc‐related Tamworth Belt of the southern New England Orogen, eastern Australia, and is now located in an apparently allochthonous position outboard of the subduction complex. A palaeomagnetic investigation of many rock units has been undertaken to shed light on this anomalous location and orientation of this terrane. Although many of the units have been overprinted, pre‐deformational magnetizations have been isolated in red beds of the Late Carboniferous Kullatine Formation from the northern part of the terrane. After restoring these directions to their palaeohorizontal (pre‐plunging and pre‐folding) orientations they appear to have been rotated 130° clockwise (or 230° anti‐clockwise) when compared with coeval magnetizations from regions to the west of the Hastings Terrane. Although these data are insensitive to translational displacements, a clockwise rotation is incompatible with models previously proposed on geological grounds. While an anti‐clockwise rotation is in the same sense as these models the magnitude appears to be too great by about 100°. Nevertheless, the palaeomagnetically determined rotation brings the palaeoslopes of the Tamworth Belt, facing east, and the Northern Hastings Terrane, facing west before rotation and facing southeast after rotation, into better agreement. A pole position of 14.4°N, 155.6°E (A₉₅ = 6.9°) has been determined for the Kullatine Formation (after plunge and bedding correction but not corrected for the hypothetical rotation). Reversed magnetizations interpreted to have formed during original cooling are present in the Werrikimbe Volcanics. The pole position from the Werrikimbe Volcanics is at 31.6° S, 185.3° E (A₉₅ = 26.6°). These rocks are the volcanic expression of widespread igneous activity during the Late Triassic (～ 226 Ma). While this activity is an obvious potential cause of the magnetic overprinting found in the older units, the magnetic directions from the volcanics and the overprints are not coincident. However, because only a few units could be sampled, the error in the mean direction from the volcanics makes it difficult to make a fair comparison with the directions of overprinted units. The overprint poles determined from normal polarity magnetizations of the Kullatine Formation is at 61.0°S, 155.6°E (A₉₅ = 6.9°) and a basalt from Ellenborough is at 50.7° S, 148.8° E (A₉₅ = 15.4°), and from reversed polarity magnetizations, also from the basalt at Ellenborough is at 49.4° S, 146.2° E (A₉₅ = 20.4°). These are closer to either an Early Permian or a mid‐Cretaceous position, rather than a Late Triassic position, on the Australian apparent polar wandering path. Therefore, despite their mixed polarity, and global observations that the Permian and mid‐Cretaceous geomagnetic fields were of constant polarities, the age of these overprint magnetizations appears to be either Early Permian or mid‐Cretaceous.     

Palaeomagnetic results from the ca. 1130 Ma Borgmassivet intrusions in the Ahlmannryggen region of Dronning Maud Land, Antarctica, and tectonic implications

Detailed palaeomagnetic and rock magnetic analyses provide improved palaeomagnetic results from 23 sites in the Borgmassivet intrusions in the Ahlmannryggen region of Dronning Maud Land, East Antarctica. These intrusions are of similar age to their host, the ca. 1130 Ma Ritscherflya Supergroup (RSG). A mean direction of D=235.4°, I=−7.6° with k=45.9 and α₉₅=4.5° was obtained from this study. When combined with previously reported results from 11 sites in the same region, including sites from the Ritscherflya Supergroup, it gives an overall mean direction for 34 sites from the igneous suite with D=236.5°, I=−3.6°, k=27.9 and α₉₅=4.8°. Isothermal remanent magnetization (IRM) experiments on several specimens suggest magnetite or titanomagnetite as the primary remanence carrier, while high temperature magnetic susceptibility experiments indicate the presence of single domain particles. These observations, together with field evidence and the high coercivities and unblocking temperatures, support a primary origin for the observed characteristic remanence. The Borgmassivet palaeomagnetic pole lies at 54.5°E, 8.3°N with A₉₅=3.3°. If Antarctica is moved to its Gondwanan position adjacent to southeast Africa, the Borgmassivet pole (BM) coincides with that of the African well-established, well-dated (1100 Ma) Umkondo Large Igneous Province pole, supporting the hypothesis that the Grunehogna craton of Dronning Maud Land was part of the Kalahari craton of southern Africa at ca. 1100 Ma.     

A field-scale long-term study on radionuclide transport through weathered granites at a site in southern China

A regional strategy for safety disposal of low- and intermediate-level radioactive wastes (LILW) has been implemented in China to protect humans and the environment. A joint onsite and laboratory investigation was conducted for a field site in southern China to assess the probability for safe disposal of LILW, which requires the understanding of long-term radionuclide transport behaviors under field conditions. This study presents the field-scale modeling of radionuclide transport through weathered granites for a conservative, a weakly sorbing and a strongly sorbing tracer by incorporating laboratory and field data. The field-scale radionuclide transport model was developed on the basis of a validated long-term groundwater flow model and field-measured dispersion coefficient, as well as laboratory-characterized strontium and cesium distribution coefficients in the weathered granites. The model was then used to perform the long-term transport prediction and risk assessment of radionuclide pollution for both the natural site setting and the graded site setting. Model simulation reveals that the numerical sensitivities of calculated concentrations are tracer dependent and changing with time. The conservative radionuclide is most sensitive to changes in hydraulic conductivity (K) while slightly sensitive to changes in effective porosity (φ), specific yield (μ) and longitudinal dispersion coefficient (D _L), indicating advection is the main transport process of conservative radionuclide. The weakly and strongly sorbing tracers, on the other hand, are most sensitive to changes in the distribution coefficient (K _d) and less sensitive to changes in the rest of model parameters, revealing that sorption is the main process for controlling the transport of sorbing tracers. A conservative radionuclide plume moves at an average velocity of about 54 m/a, which is too fast to be considered as safe disposal under the natural site setting. However, the plume of the conservative radionuclide could be slowed down to a velocity around 5.3 m/a due to the reduction of the hydraulic gradient under the graded site setting. Therefore, the conservative radioactive wastes could be disposed at the mid-eastern part of the site under the graded site setting because the transport path has been prolonged and thus no conservative radionuclides could migrate out of the site in a reasonable timeframe. For the sorbing tracers, however, results of the computed transport distance are 40 and 2 m at 500 years, respectively. Therefore, they can be disposed safely at the site under both natural and graded site settings. This study provides an insight to the field-scale long-term behaviors of radionuclide transport. The integrated modeling method presented in this study is most useful for the environmental impact assessment of the site conditions relevant to the safe disposal of hazardous wastes.     

Coda wave attenuation parallel and perpendicular to the Mexican Pacific coast

We calculated the quality factor, Q_c, at frequencies from 6 to 24 Hz using coda waves of 97 aftershocks of the Petatlan, Mexico, earthquake (March 14, 1979; M_S=7.6). The data were recorded parallel (between Acapulco and Playa Azul) and perpendicular (between Petatlan and Mexico City) to the coast. The results are the following: at 12 and 24 Hz there is no significant difference in the attenuation (Q_c⁻¹) along the two paths; at 6 Hz, Q_c⁻¹ has a large scatter in both directions. This observation indicates strong site effects at this frequency; average Q_c⁻¹ is slightly higher between Petatlan–Acapulco (toward SE) than between Petatlan–Playa Azul (toward NW); and at high frequencies, Q_c⁻¹ remains essentially constant perpendicular to the coast. These results show that the large seismic wave amplifications in Mexico City are caused by shallow site effects.     

Archaeomagnetic dating of seven archaeological fireplaces in the Netherlands

The palaeomagnetic directions of seven Dutch fireplaces are compared with the archaeological age estimates which range from the first to the 17^th century AD. A comparison with the British master curve of secular variation for archaeomagnetic dating results in a refinement of the archaeological age estimates in two cases, while four other archaeological age estimates can be confirmed. For one fireplace only one sample is reliable, resulting in a very poorly defined archaeomagnetic age of 2 to 3 centuries younger than the expected age (i.e. late Middle Ages). On the other hand, accepting the archaeological age estimates, the palaeomagnetic directions can contribute to the database that is used to construct the British secular-variation master curve. We applied the classification grades proposed by Tarling & Dobson (1995) which range from unreliable (grade 1) to reliable (grade 5). Three fireplaces have grades 5, one has grade 4, one grade 3, one grade 1 and for one case no grade was assigned.