Stable Rocks Research Articles

Subsurface Microbial Colonization at Mineral-Filled Veins in 2-Billion-Year-Old Mafic Rock from the Bushveld Igneous Complex, South Africa

Recent advances in subsurface microbiology have demonstrated the habitability of multi-million-year-old igneous rocks, despite the scarce energy supply from rock-water interactions. Given the minimal evolution coupled with exceedingly slow metabolic rates in subsurface ecosystems, spatiotemporally stable igneous rocks can sustain microbes over geological time scales. This study investigated a 2-billion-year-old mafic rock in the Bushveld Igneous Complex, South Africa, where ultradeep drilling is being executed by the International Continental Scientific Drilling Program (ICDP). New procedures were successfully developed to simultaneously detect indigenous and contaminant microbial cells in a drill core sample. Precision rock sectioning coupled with infrared, fluorescence, and electron microscopy imaging of the rock section with submicron resolution revealed microbial colonization in veins filled with clay minerals. The entry and exit of microbial cells in the veins are severely limited by tight packing with clay minerals, the formation of which supplies energy sources for long-term habitability. Further microbiological characterization of drilled rock cores from the Bushveld Igneous Complex will expand the understanding of microbial evolution in deep igneous rocks over 2 billion years.

Модернизация технологий месторождений оловянных руд с учетом ретроспективной оценки опыта восстановления потенциала предприятий

The article describes the experience of restoring the potential of enterprises in the tin industry of the Khabarovsk Territory and the Chukotka Autonomous Okrug in difficult mining and geological conditions. The purpose of the study is a retrospective assessment of the experience of improving the technology of mining tin ores in stable rocks. Materials and methods. The goal is achieved through comprehensive research, including analysis and synthesis, comparison of calculated and experimental data, calculations of mass control parameters and measures to improve the quality of ores. Results. The characteristics of the deposits and the features of their location and ore extraction are given. The parameters of the applied development systems with differentiation into variants are detailed. A scheme of options is given with a critical analysis of their advantages and disadvantages so that they can be reproduced in similar conditions. Discussion. The effectiveness of the integration of ore mining processes and equipment for their implementation is shown. The experience of using an arsenal of systems for the development of shallow and inclined deposits in stable host rocks is described. The experimentally obtained dependences of the size of the pillars on the fall of the ore body and the spans of the mine are given. The variants of a promising chamber development system with the delivery of ore by the force of an explosion are detailed. Conclusion. It is shown that the development of tin deposits with the integration of the capabilities of technological processes and equipment ensures effective development of the field while improving the safety of mining operations and extraction of minerals from the subsurface. Resume. It is concluded that the integration of mining processes and equipment for their implementation is a reserve for the implementation of the production program, and the experience of developing tin deposits can be in demand when modernizing existing technologies and designing new deposits of solid minerals. Suggestions for practical applications and directions for future research. Future research will be aimed at addressing issues related to reducing ore losses and dilution, improving the rock pressure management system and increasing the environmental and economic efficiency of the enterprise.

Analysis of Pile Foundation for Hospital Buildings

Pile foundations are widely employed to provide support for bridges and various structures, ensuring the safe transfer of structural loads to the ground while preventing excessive settlement or lateral movement. They excel in transferring structural loads from weaker or compressible soil layers to the stronger, more stable soils and rocks beneath. Pile foundations constitute an integral component of a structure.  In this research work the foundation of the hospital (G+6) was design by the pile foundation. We have used M25 grade of concrete for the preparation of design mix. The characteristic strength and load bearing of soil was tested by Plate load test and other materials tested by slump cone test , aggregate Impact Value test cement compressive strength test (cement fineness test construction water PH value . The expected result of SBC is 20000kg approximate.  Project reports typically encompass introductions and problem definitions, along with literature reviews pertinent to the project. They detail the study area's location and the project site, as well as providing concise information about the equipment utilized on- site.  Additionally, it covers crucial tasks such as centerline marking, boring, reinforcement placement, concrete pouring, excavation, and chipping of pile caps.

On the use of weathered rocks in road pavements: An experimental study on Tazekka schists

In Morocco, the management of materials in the road sector is framed by a panoply of technical and normative standards including the Moroccan guide of road earthworks dating from 2002. This document was inspired by its French counterpart and dictates the rules for soil reuse in embankments constituting an important part of the pavement structures. In fact, this document made the use of friable rocks (R category) complicated and leaves to the geotechnical engineer the definition of the necessary precautions. This ambiguity often discourages the administrative services from considering these materials as a reusable deposit and consequently they resort to more stable soils or rocks. This work illustrates the results of an experimental campaign carried out at the level of the Taza Province on several schistose massifs. The conclusions indicate the possibility of reusing these materials by adapting them through secondary treatment. In addition, the laboratory tests carried out on 250 samples from 35 different sites indicate the possibility of using these schists as road aggregates for low traffic roads constituting 70% of the provincial network of Taza. In addition, the treatment of this rock via hydraulic binders constitutes a promising and viable solution allowing its reuse in backfill and roadway subgrades. Indeed, the findings have shown that reduced proportions can significantly improve the behavior of schists and reduce their sensitivity to erosive factors.

Assessment of instability initiation in exposed salt rock roofs

Stability of rocks is the main requirement for the safe operation of mines. For this purpose, certain measures are applied for the protection and support of underground openings, including roof support design and roof arrangement in the most stable rocks. Stability assessment of underground excavations is largely related to their roof stability. Determination of possible instability conditions in mine roofs governs the choice of support system design and parameters of mine excavations. The Upper Kama Potash Salt Deposit represents a stratified layer of solid salt rocks. Roof instability develops as stratification and roof collapse. The Mohr–Coulomb criterion of coherent rocks is currently used to estimate parameters of a possible damage zone in the exposed roof. This criterion allows evaluating shear plane angles in roof rocks and, as a result, finding parameters of the possible collapse zone. The experience of mining operations in the Upper Kama deposit shows different failure conditions as against the Mohr–Coulomb criterion as the stress state is scarcely included in the criterion used. This study is an attempt to assess parameters of rock exposures by solving a Lame problem in terms of a single mine excavation. The analytical results were compared with the parameters obtained from the plane elasticity solutions by the finite element method. Based on the implemented studies, an engineering approach is developed for the assessment of anticipated instability parameters in exposed roofs in horizontal excavations driven in salt rocks.

Unit weight patterns of overlying rocks above commercial-value salt strata in the Upper Kama deposit

Stability of rocks is the main requirement for the safe operation of mines. For this purpose, certain measures are applied for the protection and support of underground openings, including roof support design and roof arrangement in the most stable rocks. Stability assessment of underground excavations is largely related to their roof stability. Determination of possible instability conditions in mine roofs governs the choice of support system design and parameters of mine excavations. The Upper Kama Potash Salt Deposit represents a stratified layer of solid salt rocks. Roof instability develops as stratification and roof collapse. The Mohr–Coulomb criterion of coherent rocks is currently used to estimate parameters of a possible damage zone in the exposed roof. This criterion allows evaluating shear plane angles in roof rocks and, as a result, finding parameters of the possible collapse zone. The experience of mining operations in the Upper Kama deposit shows different failure conditions as against the Mohr–Coulomb criterion as the stress state is scarcely included in the criterion used. This study is an attempt to assess parameters of rock exposures by solving a Lame problem in terms of a single mine excavation. The analytical results were compared with the parameters obtained from the plane elasticity solutions by the finite element method. Based on the implemented studies, an engineering approach is developed for the assessment of anticipated instability parameters in exposed roofs in horizontal excavations driven in salt rocks.

Substantination of hydromechanical parameters of water regulation using mine pillars during mines closure

Purpose. Substantiation of hydromechanical parameters that make it possible to control the safe ratio of hydrodynamic levels in a mine shaft and a rock mass when closing mines using submersible pumps. Research methodology. An experimental-analytical method was used, which consists in the formation and analysis of data from field tests of fractured porosity, permeability and the position of groundwater levels in hard sandstones around mine shafts with concrete support. Research results. It has been established that the hydromechanical state around a mine shaft in stable water-bearing rocks is characterized by the development of mutually competing processes of nonlinear decrease in the permeability of the loaded rock contour and hydrogeomechanical unloading of structural elements of water-bearing rocks and filter attachment. The values of the hydrogeomechanical unloading of the shaft attachment in the range of 0.054 - 6.125105 Pa are close to the tensile strength limit of the "concrete-water-bearing rock" contact, which indicates the danger of its collapse. Scientific novelty. The problem of combining the elastic viscometric load of the rock mass attachment and the hydrodynamic planar-radial flow to the wellbore is solved, where the hydrogeomechanical state in stable water-bearing rocks is characterized by the development of mutually competing processes of nonlinear decrease in the permeability of the loaded rock contour and hydrostatic unloading of structural elements of the water-bearing rocks and filters. Practical value. The obtained solutions and their analysis explain the discrepancy between the calculated (standard) loads on the fastening, which is known from practical experience, and actually measurable values, and also have significant practical significance. The established fact of the approximation of the value of hydrogeomechanical unloading of the stovol attachment to the tensile strength of the contact "concrete - water-bearing rock" is dubious and requires a decrease in the hydrodynamic deflection to the mine stovol when controlling the process of flooding with submersible pumps.

Experimental Investigation on the Propagation of Hydraulic Fractures through Coal‐Rock Interfaces

Although hydraulic fracturing has been one of the primary stimulation methods for coal‐bed methane (CBM) exploration, it is difficult to be applied in soft and low‐permeability coal seams due to the instability of wells in such geological structures. In order to solve the problem, an idea of indirect fracturing is proposed, that is, fractures are initiated in stable and hard rocks and then propagated to coal seams in which crack networks can be formed. To verify the feasibility of such an approach, the true triaxial hydraulic fracturing experiments were conducted using two‐dimensional and three‐dimensional coal‐rock combination samples, respectively. This study investigates the fracture patterns, pressure variation, and fracture morphology. The results show that in the process of fracture propagation from sandy mudstones to coals, the strain energy release rate in the sandy mudstones is 10.69∼25.53 times greater than that in the coal. When the fracture has a tendency to deflect toward the lower strength coal strata, under the condition of large K2/K1, the deflection criterion will be met first and the fracture will deflect and grow into the coal strata. In addition, the complex crack network can be generated when the hydrofracture intersects the coal‐rock interface and the fracture pattern is analyzed.

Insights on spatial variography and outcrop-subsurface relationship of sandstone reservoir properties: A case study from the Late Triassic Minjur Formation, central Saudi Arabia

Understanding the variography of outcrop properties may give a guide for predicting the subsurface reservoir quality, more significantly for the more stable and resistant reservoir rocks such as sandstones compared to the carbonates. This study was planned to investigate the lithofacies and reservoir properties of different sandstone lithofacies of the Late Triassic Minjur Formation outcrop, and attempted to develop a relationship between these aspects in outcrop and subsurface settings. Based on the field and petrographic analyses, sandstone lithofacies of Minjur Formation were categorized into five types upon their textures. These lithofacies were intensively investigated for porosity and permeability. Variography analyses were applied on composite outcrop lithofacies, and also on porosity and permeability data. A good relationship was observed between porosity and permeability, which coincides with the univariate statistics of each and confirmed by variography analysis. Combination of outcrop and subsurface reservoir properties showed an acceptable correlation between outcrop reservoir properties and data from central Saudi Arabia and Rub’ Al-Khali Basin in southern and southeastern Saudi Arabia. This correlation was further highlighted by the global sense of subsurface sandstone reservoir properties. In general, the current study reflects the possibility of sandstone outcrop data to act as a representative analog for its equivalent subsurface reservoir. This possibility, which is mainly controlled by the similarity in depositional setting, can be also attained for reservoir properties and quality. Obtaining more qualitative and quantitative data is always advantageous to get better and more robust correlation.

Some New Correlations of Q-Value with Rock Mechanics Parameters in Underground Oil Storage Caverns

Q-system is a preferred alternative method of rock mass classification for underground oil storage caverns where stable lithological rocks are widely distributed. In this paper, correspondences between important input rock mechanics parameters (friction angle, cohesion, tensile strength, Poisson’s ratio, deformation modulus) and Q values were investigated, thereby bringing convenient to rapidly obtain available parameters when it’s hard to collect measured field data in underground storage projects basically with similar lithology. The proposed correlations were verified through numerical simulation and on-site monitoring measurement. In addition, comparison of different criteria among Q-system and other codes for rock mass classification has been made to help for making a preliminary evaluation of rock mass quality in the practical engineering. Finally, the behaviours of surrounding rock deformations under different Q values were analysed by using FLAC3D code with the calculating parameters suggested in this paper, and the calculation results match well with measured values in situ. Above results will not only guide the construction but also could be relevant to other underground storage engineering under similar geological conditions.

Late Triassic adakite‐like volcanic rocks in Moguqi area in the central Great Xing'an Range, NE China: Implications for partial melting of delaminated thickened crust

Adakite‐like volcanic rocks in the Moguqi area of the central Great Xing'an Range of NE China consist of trachyandesites and trachydacites. These rocks yield LA–ICP–MS U–Pb zircon ages of 229.5–232.6 Ma. These adakite‐like rocks are high in Sr (459–1960 ppm) and MgO (1.2–4.3%), low in Y (11.4–23.70 ppm) and Yb (0.88–2.07 ppm), and have high Sr/Y ratios (37.17–146.31) and high Mg# values (0.43–0.58). These characteristics are similar to those of rocks derived from slab melting. However, the existence of Early Triassic stable continental sedimentary rocks of the Laolongtou Formation does not favour this mode of formation. The zircon εHf(t) values of the samples range from +8.09 to +13.29, indicating the primary magmas were generated by partial melting of juvenile crust. Analysis of geophysical data, combined with the previously published history of the Hegenshan–Heihe Suture in this region and the southward subduction of Mongol–Okhotsk oceanic plate, suggests that the Late Triassic adakite‐like volcanic rocks in the Xing'an Massif formed from the partial melting of delaminated thickened crust in an extensional setting. This occurred after orogenesis involving the Xing'an Massif and the Songnen Massif and was influenced by southward subduction of the Mongol–Okhotsk oceanic plate.

The Study of Derinkuyu Underground City in Cappadocia Located in Pyroclastic Rock Materials

Its aim is to provide a case study of the historical underground city built for up to 20 thousand people. This is a very specific, building-urban concept that is tied to the extraction of tuff rock building materials. These pyroclastic material ejected volcano in contact with Anatolian and Arabian tectonic plates. For the construction of the city were used exceptional boundary conditions. It is a fact that we have easily extractable building material which is self-supporting, and he does not need additionally reinforced. It means that these soft and stable rocks allowed the creation of large cavern system with a complete infrastructure that needed this underground city. It was placed in it both the living area and warehouse, educational, religious, wells, ventilation systems or stables for animals. There were in the in Cappadocia region up to 36 cities. The exact number depends on the classification criteria that were used.

Preservation of Urban Historic Centers

The subway construction in St. Petersburg is a very important challenge for the development of the city. The existing stations are dramatically deficient, especially in the city's bedroom suburbs. The end stations are overloaded, and parallel subway lines have to be built to relieve the available ones. The subway in St. Petersburg is mainly a deep-level one, as stable water-free rocks (Proterozoic clays) are at depths of over 40 m. Located higher are unstable aqueous sand-clay Quaternary varieties prone to frost heave, and parent Upper Vendian clays, characterized by fissures and sandstone interbeds of varying thickness. But even at significant bore depths, ground surface movements occur on large areas covering several hectares of the city's territory. The current technology of construction of subway station hubs and inclined escalator tunnels lead to significant deformations of the overlying rock and of buildings and structures erected on it, sometimes resulting in loss of structural strength and full decommissioning of buildings. The rehousing of dangerous buildings and their repair require sizeable funds and time for reconditioning of the buildings. This is especially intolerable for subway construction in the historic center of the city when memorial buildings and samples of architecture are subjected to total destruction. For instance, during the construction of the exit to the Griboyedov Canal from Nevsky Prospekt Station, one half of a historic building was dismantled, and for the construction of the surface concourse of Admiralteiskaya Station, an available house had to be totally pulled down, with a new one having similar facades erected in its place later. Therefore, extremely important is development and implementation of proposals to prevent intolerable deformations of existing buildings and structures in the construction of the subway and other underground facilities in the central districts of St. Petersburg. To solve the problem of ground surface deformation, an integrated approach is needed, comprising low-subsidence sinking techniques with parallel geotechnical monitoring including monitoring of low-depth displacements of the surrounding rocks, both in the vertical and horizontal plane.

Field measurement and failure forecast during the remediation of a failed cut slope

A large number of deep cuts are formed during the construction of expressways in mountainous areas. Inadequate interpretation of ground conditions is a major contributing factor to the failure of cut slopes. This study focuses on the Hongyan landslide along the S26 expressway. Due to lack of an adequate pre-construction investigation, a landslide was triggered by small-scale excavation at the toe part of the slope. The potential slip surface was incorrectly located; consequently, two rows of stabilizing piles were not long enough to reach stable rocks. To overcome the mistake, two additional rows of piles were installed. During construction, both slope deformation and the stress of reinforced bars in piles were monitored for safety considerations. A Verhulst model-based failure forecast was also utilized to insure the stability of the slope during remedial works. Reviewing this landslide reveals a number of lessons. First, sufficient geological investigation and careful interpretation of ground conditions are mandatory prior to the design of a cut slope. Second, systematic field monitoring is strongly recommended, especially when the geology of the slope is complex and it is difficult to determine failure patterns. Third, the failure forecast can serve as a supplementary measure to insure the safety of workers and slopes. Last, it always takes some time for stabilizing piles to mobilize.

Sequestration of atmospheric CO2 in global carbon pools

Sequestering atmospheric CO2 is necessitated by its present concentration of 385 ppm and increasing at the rate of 2 ppm y−1. Increase in atmospheric emission of CO2 with the attendant global warming and environmental degradation are driven by global energy demand. In comparison with the emission of 300 Pg C between 1850 and 2000, total emission during the 21st century is estimated at 950 to 2195 Pg, with an annual rate of emission of 20 to 35 Pg C y−1. Reduction of CO2 atmospheric loading can be achieved by biological, chemical and technological options through either reducing or sequestering emissions. This article describes technological options of sequestering atmospheric CO2 into other global pools. Geologic sequestration involves underground storage of industrially emitted CO2 into the geosphere for long-term and secure storage. Liquefied CO2 is injected about 1000 m below the ground surface either in stable porous rocks, oil wells, coal beds, or saline aquifers. Co-injecting CO2 along with H2S and SO2 is also possible. Over time, the trapped CO2 reacts with minerals to form carbonates, enhances oil recovery, or displaces coal bed methane. Deep injection of CO2 under the ocean creates a CO2 lake which eventually penetrates into the sediments. Iron fertilization is another technique of enhancing the C pool in marine biota, notably phytoplankton. The so-called “biological pumping” is based on the “iron hypothesis” of transferring C to the ocean floor. Terrestrial C sequestration is based on the natural process of photosynthesis. Transfer of CO2 into the biotic pool and soil C pool via humification and formation of secondary carbonates has numerous ancillary benefits through enhancement of ecosystem services. Soil C sequestration is essential to improving soil quality, increasing use efficiency of agronomic input, and advancing world food security. It is also needed to improve water quality by filtration and denaturing of pollutants, and enhancing biodiversity by saving land for nature conservancy. Soil C sequestration is a low hanging fruit, and a bridge to the future until low-C or no-C fuel sources take effect.

Effect of salt crystallization on stones of historical buildings and monuments, Konya, Central Turkey

In this study, we investigated the chemical and physical properties of the volcanic rocks used as building stones in historical places and monuments. The chemical weathering effect of salt crystallization on these stones was measured on the laboratory conditions (in most cases, used samples were very small). For this purpose, the dry weight loss (DWL) test was conducted. The rocks of dacite, andesite and tuffs of volcanic origin have different durability against salt crystallization. The most stable rocks are dacites (DWL 2.06%) which were used in the construction of Hittite monuments at Eflatun. The durability of the stones is closely related to their chemical, mineralogical, petrographical and mechanical properties. The stones used in the historical buildings are generally much more stable than present-day building stones.

Athyrium distentifolium Tausch ex Opiz (A. alpestre (Hoppe) Rylands ex T. Moore‐non‐Clairv.) including A. distentifolium var. flexile (Newman) Jermy

Woodsiaceae. Athyrium distentifolium, Alpine lady-fern. Fronds bi-pinnate, ovate-lanceolate, yellow-green 20 cm to over 100 cm, arising in a 'shuttlecock' from a central crown. Stipe straight, one fifth to one quarter the length of the blade with pale brown scales, usually broad, but occasionally narrow. Pinnae widely spaced near base of the frond, and sometimes deflexed, crowded near the tip, meeting the rachis at an angle of 900 at the midpoint of the blade, or slightly ascending. Pinnules broadest at the base, tapering to a point. Sori circular, with irregular filaments making up a rudimentary indusium when young, soon obscured as the sori grow. Sori concentrated in the upper part of the frond, becoming sparse towards the base. Number of sori varies with size of frond. Plants frequently infertile (McHaffie et al. 2002). Athyrium distentifolium var.flexile Newman's lady-fern. Fronds bi-pinnate, narrow, blue-green, 10-40 cm, arising from a central crown, erect or sharply angled near the base of the rachis to lie nearly flat against the substrate. Stipe short, one sixth to one eighth the length of the blade, often densely covered with broad, pale scales that may continue beyond the midpoint of the blade. Blade broadest near the base, or nearer the mid-point. Pinnae close together near base of frond, often strongly deflexed to at least half way up the frond. Uppermost pinnae widely spaced. Pinnules taper towards the base. Sori circular, sometimes with only a few sporangia; rudimentary indusium visible while the sorus is still immature. Sori concentrated at base of the frond, becoming less frequent towards the tip. Plants usually fertile (McHaffie et al. 2002). Athyrium distentifolium is a chionophilous fern that grows at altitudes or latitudes which ensure long-lying winter snow cover. Deep snow provides insulation from severe winters, and prevents early growth in a mild spring. Only a limited number of species can tolerate these conditions and this reduces competition. Although previously known as a Scandinavian and continental European species, A. distentifolium was not recognized in Britain until 1844 (Newman 1851). Within Britain it is found only in Scotland where it is confined to the remote Highlands. Soon after it was identified, another similar taxon of uncertain taxonomic status was described (Backhouse 1852). Subsequent research has determined that this is a recessive variety which is now known as A. distentifolium var.flexile. Both taxa are covered in this account.

Specific Features of Lithological and Mineralogical Compositions of Moraines in the Don Region

Results of the detailed lithological-mineralogical study of moraines from the well-known key sections in the Don Basin are presented. Important debatable issues concerning the age of Early Pleistocene glacial sediments are considered. Together with biostratigraphic data, recent data on the mineral composition of key moraine units can be used for solving these issues. The layered moraine sequence of the Don Basin (hereafter, Don moraine) shows compositional similarity in a regional scale. However, it is characterized by a spatiotemporal variation in the mineral and petrographic associations governed by specific paleogeographic settings and stages of moraine formation. Specific features of temporal rearrangement of these associations indicate the general paleogeographic trend of glacial lithogenesis. Therefore, they make it possible to compare moraines from the Kuznetsovka and Vol’naya Vershina sections that include a combination of the most stable (and, generally, local) minerals and rocks of early stages of glacial lithogenesis. The compositionally most exotic Novokhopersk and Moiseevo moraines are logically attributed to the later stage of moraine formation. This does not contradict specific features of teriofauna in the interglacial sediments underlying and overlying the moraines. It is shown the spatiotemporal variation in the mineral composition of moraines of the Don region can be used for their stratigraphic correlation.

Petromagnetic characteristics of Cameroon Line volcanic rocks

Volcanic rock samples collected from 154 sites on the Cameroon Line (CL) have been analysed to study their petromagnetic characteristics. Thermomagnetic experiments and electron microscope observations on the samples indicate that the principal magnetic mineral and carrier of Natural Remanent Magnetisation (NRM) in these rocks is titanomagnetite rich in titanium. These also indicate that the level and stability of magnetisation are dependent on the quantity and composition of the magnetic minerals (which are controlled by the composition of the original liquid magma), their oxidation states and grain sizes. The contribution of high- and low-temperature oxidation observed in some of the magnetic minerals was that of increasing their magnetic resistance. Rocks with abundant ilmenite lamellae in their titanomagnetite showed increased magnetic resistance during demagnetisation experiments. In the analysis, the samples exhibited a considerable magnetisation spectrum indicating that most of them are strongly magnetic. The general tendency in experimental magnetism of an increase in magnetic resistance with decrease in grain sizes of discrete magnetic minerals is not respected in this natural system because of the effects of the presence of many ilmenite lamellae and mini-fractures in some of the titanomagnetite grains. In this way, the conditions of low crystallisation temperature, high f O2 and high P H 2O , which were the conditions for the crystallisation of the most stable rocks (the hawaiites) on the line, were the conditions favourable for the acquisition of a stable magnetisation in the region. The low Curie temperatures (74–250 °C) found for a majority of the rocks indicate that the lower crust in the region and the upper mantle could be nonmagnetic. The high regional negative magnetic anomaly over the Cameroon Line that is not consistent with the small depth previewed by the Curie system and by the paramagnetic effect of the acid volcanic rocks in the region is probably derived principally from the differentiated basalts.

First Palaeogene sedimentary rock palaeomagnetic pole from stable western Eurasia and tectonic implications

A palaeomagnetic investigation of lower Eocene (ca. 52 Ma) London Clay Formation cemented mudstones from Sheppey (SE England) has yielded a mean direction of Dec. = 1.1, Inc. = 43.2°, where N = 9, a95 = 6.8° and K = 58.5.This apparently high-quality direction (Q-factor = 5) has an associated palaeopole of 178.6°E, 63.7 N, where A 9 5 = 6.8°. The data represent the first pole from post Jurassic stable Eurasia rocks outside of the European North Atlantic Igneous Province (NAIP), of which most results have been obtained from NW Britain and the Faroe Islands. The data can in part be used to constrain the position of Palaeogene Eurasia, in particular the zero-offset declination implying negligible rotation of western Eurasia since the early Cenozoic. This is in contrast with data derived from the European NAIP, which imply small to moderate clockwise rotations for this part of the plate. The inclination angle may provide less useful information as it appears to be anomalously shallow when compared with that associated with the NAIP derived poles. In an attempt to understand the shallowing, we re-examined data from Palaeocene-Eocene sediments recovered in several boreholes (bathyal sediments in DSDP Hole 550, four cores through fluvio-delatic to middle shelf sequences in the London area, and one borehole sequence from East Anglia). In all cases, the sediments show systematic inclination shallowing similar in magnitude to that reported from Sheppey. Tectonic and geomagnetic explanations can be discounted; sediment compaction appears to be the likely cause. In light of the current controversy surrounding the 'stable Asia shallow inclination problem', the result reinforces the suggestion that tectonic modelling needs to he done carefully when the supporting data are based exclusively on palaeomagnetic studies of sedimentary rocks.