The total REE content varies from 100 to 1300 ppm. An average of the similar fraction of 16 non-marine clays, mostly tillitic, gave 527 ppm REE. An average of 38 glacial and postglacial marine clays from the lower part of the Numedal valley gave 335 ppm REE (max. 781 ppm). After removal of adsorbed ions the average total REE content of morainian and marine clays decreased to 186 ppm.
The content and distribution of the REE in the Numedal clays are strongly influenced by environmental factors. Under neutral and alkaline conditions the REE are accumulated by adsorption on clay minerals, and by increasing the hydrogen ion concentration the adsorbed ions are readily removed. 相似文献
The index properties of both clays are similar and, accordingly, their strength parameters are mutually close. Test results of the more compact and less wet clay (WB) are affected by the sampling and trimming procedures, especially for 38 mm diameter specimens.
Although the behaviour is similar, the origin of fissures is different. For the SM clays, weathering is the main cause and fissuring reaches a depth of about 20 m. WB clays are dissected by macro- and microfissures originating as the result of tectonic processes and volumetric changes (effect of the coal formation underneath the investigated massif).
Cementation of some samples was found and the transition from clays through cemented clays to claystones (soft rocks) is speculated. 相似文献
The deepest (4,100 m) dredge haul contains deeply weathered coarsegrained igneous rocks. Nine other hauls, distributed between 4,000–2,300 m, contain holocrystalline basalts and diabases. The compressional wave velocity of air-dried samples of two holocrystalline basalts and a diabase at atmospheric pressure ranges from 5.0–5.6 km/sec. Sampling in depths less than 2,300 m shows that the crest of the Beata Ridge is capped by Quaternary deposits underlain by consolidated carbonate sediment of at least Middle Eocene age. The faunal assemblages of the Mid-Eocene samples are the product of normal accumulation in a shallow shelf environment.
The dredging results coupled with previously published seismic reflection and refraction data, suggest that the 5.4–5.7 km/sec crust is composed of a layer of basalt and diabase which outcrops below 2,300 m, on a fault-generated escarpment that was produced in the Late Cretaceous-Early Tertiary. The shallow shelf samples of Eocene age indicate that the Beata Ridge was higher in the Early Tertiary and has subsided subsequently to its present depth. 相似文献
The evolution of the area is influenced by a number of factors: (1) thermal subsidence centred in the central North Sea providing accommodation space for thick sediment deposits; (2) 250-m eustatic fall from the Late Cretaceous to present, which causes exhumation of the North Sea Basin margins; (3) varying sediment supply; (4) isostatic adjustments following erosion and sedimentation; (5) Late Cretaceous–early Cenozoic Alpine compressional phases causing tectonic inversion of the Sorgenfrei–Tornquist Zone (STZ) and other weak zones.
The stress field and the lateral variations in lithospheric strength control lithospheric deformation under compression. The lithosphere is relatively weak in areas where Moho is deep and the upper mantle warm and weak. In these areas the lithosphere is thickened during compression producing surface uplift and erosion (e.g., at the Ringkøbing–Fyn High and in the southern part of Sweden). Observed late Cretaceous–early Cenozoic shallow water depths at the Ringkøbing–Fyn High as well as Cenozoic surface uplift in southern Sweden (the South Swedish Dome (SSD)) are explained by this mechanism.
The STZ is a prominent crustal structural weakness zone. Under compression, this zone is inverted and its surface uplifted and eroded. Contemporaneously, marginal depositional troughs develop. Post-compressional relaxation causes a regional uplift of this zone.
The model predicts sediment distributions and paleo-water depths in accordance with observations. Sediment truncation and exhumation at the North Sea Basin margins are explained by fall in global sea level, isostatic adjustments to exhumation, and uplift of the inverted STZ. This underlines the importance of the mechanisms dealt with in this paper for the evolution of intra-cratonic sedimentary basins. 相似文献
Kaolinite hydrogen isotope ratios of two large residual economic deposits (Tirschenreuth: δDSMOW=−80‰ to −76‰; Hirschau–Schaittenbach: δDSMOW=−70‰ to −63‰) can be used in combination with additional geological evidence to constrain the timing of weathering in these areas. A late Early Cretaceous kaolinization age is suggested for the Early Triassic sandstone-hosted deposits near Hirschau–Schnaittenbach, whereas a Late Oligocene to Mid-Miocene age is indicated for the Carboniferous granite-hosted Tirschenreuth deposits. 相似文献
The thirty types of rocks are divided into nine groups according to their petrological and road engineering properties. In some cases this grouping cuts across the traditional genetic classification of rocks.
Special attention is drawn to the importance of quartz in determining the quality and durability of rock to be used as aggregate in road construction. 相似文献
The tsunami deposits display many sub-layers with scoured and graded structures. Each sub-layer, especially in sandy facies, is characterized by HCS and inverse and normal grading that are the result of deposition from prolonged high-energy sediment flows. The vertical stack of sub-layers shows incremental deposition from the repeated sediment flows. Mud drapes cover the sub-layers and indicate the existence of flow-velocity stagnant stages between each sediment flow. Current reversals within the sub-layers indicate the repeated occurrence of the up- and return-flows.
The tsunami deposits are vertically divided into four depositional units, Tna to Tnd in ascending order, reflecting the temporal change of wave sizes in the tsunami wave trains. Unit Tna is relatively fine-grained and indicative of small tsunami waves during the early stage of the tsunami. Unit Tnb is a protruding coarse-grained and thickest-stratified division and is the result of a relatively large wave group during the middle stage of the tsunami. Unit Tnc is a fine alternation of thin sand sheets and mud drapes, deposited from waning waves during the later stage of the tsunami. Unit Tnd is deposited during the final stage of the tsunami and is composed mainly of suspension fallout. Cyclic build up of these sub-layers and depositional units cannot be explained by storm waves with short wave periods of several to ten seconds common in small bays. 相似文献
The existence of opal saturated lagoons, as inferred from the “box-work geodes”, suggests that much of the replacement chert, porcelanite, and silicified fossils in the Tertiary deposits of peninsular Florida formed in the shallow subsurface. Subsequent weathering of carbonates and clays not encapsulated in the box works has resulted in formation of a green montmorillonite residual clay bed. 相似文献
An overall transgressive pattern is shown by the general trend of the depositional setting, which evolved from flashy alluvial fans, through multiple-channel bedload rivers, mixed-load sinuous rivers, terminal fans, coastal sabkha and evaporitic lagoon, to a shallow, low-gradient marine ramp. The inferred fluvial regime was subject to rapid and erratic fluctuations in discharge. Palaeosols are represented by calcic soils, and suggest a warm to hot, semi-arid or dry subhumid climate with strongly seasonal rainfall. Vertic features are associated with more inland alluvial complexes: they are missing in the terminal-fan deposits, suggesting greater aridity in lowland (coastal) areas.
The Bellerophon Fm. consists of two units: a lower evaportte-bearing unit, deposited in a barred basin, and an upper shallow-marine carbonate unit, laid down on a very low-energy, low-gradient ramp.
Five third-order sequences and the lower part of a sixth sequence, collectively showing a backstepping pattern, have been identified in the succession. Due to the presence of a very low-gradient ramp margin, and the consequent ineffectiveness of relative sea-level falls in producing large-scale erosion in coastal areas, it is suggested that, rather than eustatic changes, degradational episodes marking sequence boundaries in the red-bed succession reflect changes in the climate-modulated intrinsic variables of discharge and sediment supply, and/or tectonic uplift.
Base level rises in, red-bed sequences are recorded by upward change from thick channel-belt sandstone bodies with an often high connectedness ratio, to progressively thinner channel deposits, ranging from isolated ribbons to channel-belt sandstone bodies potentially reaching high width/thickness ratios, encased in a comparably greater volume of overbank fines. This trend is thought to reflect the change from a confined geomorphic setting, with a limited area of potential avulsion, to an unrestricted setting with rivers free to move extensively; in addition, it documents the transition from an inland fluvial system with laterally migrating perennial or semi-perennial channels, to an ephemeral network of randomly migrating and frequently avulsing small terminal-fan distributaries, through a drastic downstream decrease in channel depth and discharge.
Identification of key sequence-stratigraphic relationships within the red-bed succession was mostly aided by the presence of easily recognizable and regionally correlated marine and marginal marine bed packages, traceable landwards into alluvial deposits showing faint traces of tidal activity, interpreted as the equivalent of marine maximum-flooding sediments. They may grade upwards into progradational fluvial packages showing basinward increase in thickness.
The Upper Permian deposits of the Southern Alps are considered part of an Upper Permian-Lower Triassic, second-order, structurally controlled sequence. The location of the basin on a thickened, previously active crust, affected by thermal perturbance after the last stages of the Variscan orogeny, the relatively reduced thickness of the basin fill, and predominantly long, transverse drainage networks, mostly derived from the denuded Insubric footwall, all suggest that sedimentation took place in a supradetachment basin, with a major detachment fault located in the palaeo-Insubric belt. 相似文献
Settlement of clay soils after freezing and thawing is the result of the suction forces that draw pore water to the freezing front. These suction forces cause an increase in the effective stress on the clay beneath the freezing front, and thus cause an overconsolidation of the clay. As these suction forces often exceed 1 atm, their direct measurement is not easy.
A technique for indirectly determining the maximum suction occurring during freezing is presented which utilizes the apparent memory that clay soils have for maximum past (preconsolidation) pressures. Suctions as large as 532 kN m−2 were observed after freezing and thawing a clay soil which was initially consolidated to 128 kN m−2.
The volume changes resulting from the freezing and thawing of clays were related to the plastic limit and were observed in the laboratory to be as high as 25%. If provisions are not made to account for these volume changes in a ground freezing project, considerable damage to structures can occur from settlement and the resulting stresses. 相似文献
This paper suggests a formulation of a model of thermo-elasto-plastic behaviour of non-expansive saturated clays characterised by two plastic mechanisms. The mechanical yield surfacefTm of the contact-stress mechanism is based on a modified cam-clay model; the thermal softening yield surfacefT is a plane separating two thermal domains. In normally consolidated conditions, the resulting response to an increase of temperature is compressive. However, in highly overconsolidated conditions, a small irreversible dilative volumetric strain is observed when the temperature is above a threshold value. In intermediate conditions, the material starts with an expansion and tends to a compression.
The constitutive model combines thermo-mechanical hardening, predominant in normally consolidated states (NCS) and absent in overconsolidated states (OCS) where the thermal softening occurs. The characterisation of the model requires information about rheological parameters obtained from oedometric and triaxial paths. Lastly, some numerical simulations of thermo-mechanical tests onremoulded Boom, ‘Bassin Parisien’ andPontida clays are presented, which show satisfactory agreement between experiments and model predictions. 相似文献
The Archean organic material shows C isotope values between −47 and −15%. vs. PDB. The Proterozoic metasediments show a smaller range, with δ13C between −30 and −17%.,
A few carbonate samples yielded C isotopic compositions between −5.9 and −4.7%.,
Associated iron sulfides have δ34S-values ranging from −6 to +8%., which are consistent with isotopic fractionation effects either by inorganic or bacterial reactions in the sedimentary sulfur cycle.
The great variability of organic C isotopic composition, especially in the late Archean, although affected by extensive postdepositional alteration, might indicate differences in the environmental conditions and/or the organic content of these sedimentary basins. Some extremely 13C-depleted organic carbon values support a global occurrence of environments likely dominated by methanotrophic organisms at the end of the Archean. 相似文献