An experimental approach for determination of the Weibull homogeneity index of rock or rock-like materials

Acta Geotechnica - The spatial variation of the physical–mechanical properties of rock or rock-like materials is an intrinsic characteristic of the materials induced by multiscale material...     

The occurrence and research potential of microfossils in inorganic archaeological materials

The microscopic remains of organisms, or “microfossils,” can occur within or attached to a range of different inorganic archaeological materials. Because of their small size, these inconspicuous phenomena can be easily overlooked. However, as this paper illustrates, the detailed biological and palaeontological analysis of microfossils in such contexts may be an important source of archaeological data. By critically reviewing a range of specialized cross‐disciplinary analyses, it is shown how microfossils can be used to provenance inorganic artifacts, reconstruct aspects of their manufacturing technology, and infer their function. © 2008 Wiley Periodicals, Inc.     

The role of liquid immiscibility in the genesis of carbonatites — An experimental study

The two-liquid field between alkali-carbonate liquids and phonolite or nephelinite magmas from the Oldoinyo Lengai volcano has been determined between 0.7 and 7.6 kb and 900°–1,250° C. The miscibility gap expands with increase in and decrease in temperature. Concomitantly there is a rotation of tie-lines so that the carbonate liquids become richer in CaO. The element distribution between the melts indicates that a carbonate liquid equivalent in composition to Oldoinyo Lengai natrocarbonatite lava would have separated from a phonolitic rather than a nephelinitic magma. CO₂-saturated nephelinites coexist with carbonate liquids much richer in CaO than the Lengai carbonatites, but even so these liquids have high alkali concentrations. If the sövites of hypabyssal and plutonic ijolite-carbonatite complexes originated by liquid immiscibility, then large quantities of alkalis have been lost, as is suggested by fenitization and related phenomena. The miscibility gap closes away from Na₂O-rich compositions, so that the tendency to exsolve a carbonatite melt is greater in salic than in mafic silicate magmas. The two-liquid field does not approach kimberlitic compositions over the range of pressures studied, suggesting that the globular textures observed in many kimberlite sills and dykes may be the result of processes other than liquid immiscibility at crustal pressures.     

Investigating the frictional response of granitic rock surface: An experimental approach

Rock friction varies as a function of mainly four parameters that are waiting time and velocity of motion between two frictional surfaces, surface roughness and normal stress. In this paper, a study on former two aspects of rock frictional behaviour has been attempted for granitic rock surface. In one experiment, waiting time for which the two surfaces remain in contact is increased from 20 seconds to 18 hours. In the second experiment, waiting time is kept constant for a series of rock slip experiments where the velocity is increased from 10??m/sec to 350??m/sec. The value of critical velocity is obtained from transformation of the stick slip motion to steady motion occurs. The relation of coefficients of dynamic and static friction with increasing velocity of motion is studied and these are used to calculate the frictional constants, namely ??a?? and ??b?? specific to the chosen simulation type.     

The development of sheath folds in viscously stratified materials in simple shear conditions: An analogue approach

Sheath folds are highly non-cylindrical folds occurring in a variety of geological settings, and have been studied using different approaches. With the present work, we provide a quantitative analysis of the generation and development of sheath folds in a viscously layered system in simple shear conditions. The sheath folds develop from an initial non-cylindrical deflection located on the highly viscous layer. The analogue experiments investigated the influence of (1) variations in the viscosity ratio between the high viscosity layer and the matrix (η_hvl/η_m), (2) variations in the ratio between the amplitude of the initial deflection and the thickness of the high viscosity layer (A_f/T_hvl), and (3) progressive simple shear (γ). The results show that increases in η_hvl/η_m will produce progressively less elongated sheath folds, while increases in A_f/T_hvl will result in more elongated sheath folds. We present regime diagrams with η_hvl/η_m and A_f/T_hvl for different shear strains illustrating under which conditions sheath folds form. In case the original deflection amplitude and layer thickness as well as γ can be retrieved for sheath folds in nature, then their geometry can be used to quantify the effective η_hvl/η_m.     

An experimental approach to the palynology of cave deposits

Surface sediment, speleothems, and bat guano from two adjacent, topographically different cave sites in eastern Spain have been studied palynologically to elucidate the potential of cave sediments for palaeoenvironmental reconstruction. A cave opening with a large entrance and constant width presented far fewer problems of alteration in the pollen assemblages than a sac‐like cave opening with a constricted entrance. Pollen concentration is linked primarily to the amount of pollen input rather than to the result of post‐depositional alteration. Sampling should be undertaken away from parietal and rear areas and avoiding moisture zones. Lateral differences in the pollen spectra indicate that sampling should be on the basis of a multiple‐profile approach and selection of dry rather than wet sediments. If these procedures are followed, within‐cave sediments can realistically reflect not only local but also regional vegetation of the site. Copyright © 2000 John Wiley & Sons, Ltd.     

An approach to model the mechanical behavior of transversely isotropic materials

The present work proposes an approach to adapt existing isotropic models to transversely isotropic materials. The main idea is to introduce equivalence relations between the real material and a fictitious isotropic one on which one can take all the advantages of the well‐established isotropic theory. Two applications of this approach are presented here: a failure criterion and a damage model that takes into account the load‐induced anisotropy. In both cases, theoretical predictions are in agreement with the experimental data. In the present paper, the developed approach is applied to sedimentary rock materials; nevertheless, it can be generalized to any material that exhibits transverse isotropy. Copyright © 2015 John Wiley & Sons, Ltd.     

Formation processes affecting submerged archaeological sites:An overview

Although the formation processes operating on submerged archaeological sites are just as varied as those affecting terrestrial ones, nautical archaeologists have not yet devoted much attention to them. Most studies to date are concerned with formation processes at particular sites. This article provides an overview of the major depositional and postdepositional formation processes affecting underwater sites. The most obvious depositional process is shipwreck, which takes several different forms. Submerged sites may also be formed by the drowning of coastal areas due to tectonic or eustatic sea level changes. In these cases, rapid submergence preserves sites better than slow inundation, which allows time for waves and currents to tear the site apart. For both shipwrecks and coastal sites, once submergence occurs, the single most important factor for preservation is rapid burial by sediment. A cover of sediment protects both the artifacts themselves and their spatial patterning from destruction by water and marine organisms. Once deposited, underwater sites are subject to modification by both cultural and natural processes. The best understood postdepositional processes include salvaging, treasure hunting, and destruction by marine borers. Others, such as dredging, construction, and bioturbation, have hardly been investigated at this time. Archaeologists need to devote more attention to the effects of marine animals that live in close association with the seabed, as well as marine plants, whose roots may disturb sites located in shallow water. From this study it is clear that maritime archaeologists must consider formation processes when planning projects, rather than thinking of underwater sites as simply “time capsules.” © 1999 John Wiley & Sons, Inc.     

Effects of pocket gopher burrowing on archaeological deposits: A simulation approach

The construction of burrows and movement of sediment by pocket gophers alter archaeological deposits by causing vertical size-sorting of artifacts, destruction of fragile artifacts, disruption of sedimentary structures, and organic enrichment of the subsurface. To evaluate the long-term effects of exposure to burrowing, a simulation was developed based on quantitative information on pocket gopher burrows and rates of sediment movement. Simulation results indicate the development of a distinct stone zone composed predominantly of particles greater than 6 cm after 4000–5000 years, and a logarithmic pattern to the rate of strata disruption. The patterns produced by the simulation compare well with patterns exhibited by actual archaeological deposits belonging to California's Milling Stone Horizon. These results suggest that current notions concerning the Milling Stone Horizon and other aspects of California prehistory may require revision, and that more emphasis must be placed on formation process research in such settings.     

The initiation and linkage of surface fractures above a buried strike-slip fault: An experimental approach

Surface fractures in the overburdened sedimentary rocks, formed above a deep-seated basement fault, often provide important information about the kinematics of the underlying master fault. It has already been established that these surface fractures dynamically evolve and link one another with progressive displacement on the master fault below. In the present study, two different series of riedel-type experiments were carried out with clay analogue models under different boundary conditions viz., (i) heterogeneous simple shear of the cover rocks above a buried strike slip fault (wrench system) and (ii) heterogeneous simple shear with a component of shear-normal compression of the overburden package above a basement fault (transpressional system), to observe the initiation and linkage of surface fractures with varying T′ (where T′ = thickness of the overburden normalized with respect to the width of the master fault). In the wrench system, Riedel (R) shears were linked by principal displacement (Y) shears at early stages (shear strain of 0.8 to 1) in thin (2 < T′ < 18) models and finally (at a minimum shear strain of 1.4) gave rise to a through-going fault parallel to the basement fault without development of any other fracture. Conjugate Riedel (R′) shears develop only within the thicker (T′ > 18) clay models at a minimum shear strain of 0.7. With increasing deformation (at a minimum shear strain of 1.2) two R′ shears were joined by an R shear and finally opened up to make a sigmoidal vein with an asymmetry antithetic to the major fault-movement sense. Under transpression, the results were similar to that of heterogeneous simple shear for layers 2 < T′ < 15. In layers of intermediate thickness (15 < T′ < 25) early formed high angle R shears were cross cut by low angle R shears (at a minimum shear strain of 0.5 and shortening of 0.028) and “Riedel-within-Riedel” shears were formed within thick (T′ > 25) models (at minimum shear strain of 0.7 and shortening of 0.1), with marked angularity of secondary fault zone with the master fault at depth.     

Role of pressure and temperature in inclusion-induced shear localization: An analogue experimental approach

Using analogue model experiments this study investigates the effects of lithostatic pressure and temperature in controlling the pattern of shear localization around rigid inclusions. Compression experiments were conducted on polymethylmethaacrylate (PMMA) by varying confining pressure (P = 30–70 MPa), homologous temperature (T_o = 0.67–0.80 corresponding to room temperature – 80 °C) and axial strain (yield – 15%) in a triaxial setup. Mechanical data showed temperature has a greater influence on the bulk yield strength and steady-state flow of the analogue material than confining pressure. Increasing confining pressures multiply the shear bands in number, and their overall pattern becomes progressively more complex, leading to composite band structures. On the other hand, under ambient pressure increasing temperature results in a transition from incipient high-strain zones to shear bands with sharp boundaries. Further increase in temperature switches the mode of shear localization, sharp to diffuse type. We finally show the inclusion-induced shear localization as a two-stage process, and provide a micro-mechanical explanation for the P-T dependent shear band patterns, attributed to three mechanically distinct domains of the inclusion-matrix interface: compression, extensional and shear localization.     

天然矿物材料修复富营养化水体的实验研究

采用底泥掩蔽技术，选取天然红土，添加适量的粉煤灰及石灰粉作为掩蔽覆盖物，对滇池富营养化水体进行现场修复实验。结果表明：用天然矿物材料减小底泥内源营养盐负荷的释放修复富营养化水体的效果良好；红土是有效的底泥覆盖材料，添加粉煤灰和石灰粉有助于消减底泥中TP、TN的释放量，还可提高对藻类等浮游植物繁殖的营养基础和对藻、藻细胞及其胚胎上浮生长的控制效率，最终达到除藻的目的，为滇池及类似湖库富营养化水体的修复提供了崭新的思路。     

Dissolution kinetics of synthetic Na-smectite. An integrated experimental approach

The effect of pH and Gibbs energy on the dissolution rate of a synthetic Na-montmorillonite was investigated by means of flow-through experiments at 25 and 80 °C at pH of 7 and 9. The dissolution reaction took place stoichiometrically at 80 °C, whereas at 25 °C preferential release of Mg over Si and Al was observed. The TEM-EDX analyses (transmission electronic microscopy with quantitative chemical analysis) of the dissolved synthetic phase at 25 °C showed the presence of newly formed Si-rich phases, which accounts for the Si deficit. At low temperature, depletion of Si concentration was attributed to incongruent clay dissolution with the formation of detached Si tetrahedral sheets (i.e., alteration product) whereas the Al behaviour remains uncertain (e.g., possible incorporation into Al-rich phases). Hence, steady-state rates were based on the release of Mg. Ex situ AFM measurements were used to investigate the variations in reactive surface area. Accordingly, steady-state rates were normalized to the initial edge surface area (11.2 m² g⁻¹) and used to propose the dissolution rate law for the dissolution reactions as a function of ΔG_r at 25 °C and pH∼9:

     

Soil proteomics: An assessment of its potential for archaeological site interpretation

In this work, two sets of experiments were carried out to assess the potential of soil proteomics for archaeological site interpretation. First, we examined the effects of various protein isolation reagents and soil constituents on peptide mass fingerprinting (PMF) of soil-like materials spiked with bovine serum albumin (BSA). In a subsequent case study, we assessed the relative age of soils from an ancient clay floor of a Roman farmhouse using amino acid racemization and then applied MALDI-TOF–MS–MS to detect and identify biomarkers for human occupation. The results from the first experiments indicate that BSA isolation efficiencies are hampered by the presence of clays and reactive organic matter (glucose), whereas these effects are, to some extent, reversed by the presence of humic acids. We also show that specific regions of the BSA molecule (the out most α-helical regions of domain 2 and 3) are more susceptible to isolation than other regions and this suggest that soil proteins can be only partly isolated. Soil–protein interactions were also found to inhibit tryptic cleavage of BSA, resulting in an enhanced specificity of BSA peptides. Our results further stress the importance of multiple or sequential protein isolation protocols with a focus on citrate and hydrofluoric acid. Results from the case study indicate that the ancient floor samples contain degraded and most likely aged proteinaceous matter, probably of keratinaceous origin.     

TRANSIT,an experimental archaeological program in periglacial environment: Problem,methodology, first results

The aim of the experimental archaeological program TRANSIT is to improve the scientific study of Paleolithic sites. This program is based on studies and experiments carried out at high altitudes in the French Alps. One of its goals is to assess the effects of periglacial processes on spatial distributions within archaeological assemblages and on artifacts and bones. Research on sedimentary environments elucidates stratogenesis in periglacial contexts. In particular, sedimentary models that are useful for interpreting fossil deposits were identified. The first results obtained from experimental artifact test plots emphasize the importance and speed of changes that occur in such a climatic and morphodynamic context. Mean lateral displacements from 1.66 to 4.75 cm yr⁻¹ were measured. Moreover, analysis of osseous and dental pieces showed that they experienced important damage. Works on pollen assemblages have shown that most of the pollen deposited on the ground surface is quickly removed and that, owing to the very uneven preservation of pollen taxa, an important distortion of the initial spectrum occurs. A model of spatial arrangement of artifacts linked to the action of solifluction processes is also proposed. Finally, application of these results to some Paleolithic sites in the Massif Central and southwest France are discussed. © 1998 John Wiley & Sons, Inc.     

Dating the course of the lower red river in Louisiana: The archaeological evidence

Archaeological data from the lower Red River in Louisiana indicate that the modern course of the river is 1200 years older than previously suggested. Geologists claim a diversion of Red River through Moncla Gap approximately 500 to 1000 years ago. Marksville period occupations dating prior to A.D. 200 are identified at archaeological sites adjacent to the river below Moncla Gap. The position of these sites on Red River levees demonstrate that they post-date the river's occupancy of the area. Extensive Marksville and later prehistoric occupations in the Moncla Gap area are seen as a direct result of the development of riverine environments resulting from this diversion.     

The significance of vivianite in archaeological settings

Vivianite is a bluish mineral sometimes encountered in archaeological deposits. It is notable for its tendency to change color from white or grayish to blue on exposure to air. Vivianite requires specific conditions for its formation—sources of iron, phosphate, and water, as well as low levels of oxygen and sulfide. Microbial activity is also thought to play a part in vivianite formation. The majority of archaeological texts do not discuss vivianite to any great degree, preventing a more detailed interpretation of site conditions and features. Vivianite was found in 25 exhumed burials from the North Brisbane Burial Ground, Queensland, Australia. Research indicated that bone or tissue samples for DNA analysis are best taken from areas distant from vivianite encrustations and that presence of vivianite has implications for artifact conservation. Vivianite at the North Brisbane Burial Grounds helped protect some skeletal and dental elements, preserved the impressions of metal coffin lacing, and also corroborated the oral history of temporary waterlogging and acted as a measure of pollution levels across the site. © 2006 Wiley Periodicals, Inc.     

An archaeological perspective of the Pleistocene/Holocene boundary in northern South America

In this paper, I examine Late Pleistocene/Early Holocene adaptations of hunter-gatherers to different ecosystems in northern South America. The role played by the climatic events associated with the Pleistocene/Holocene boundary in the evolution of culture in that part of the Americas is assessed in the light of those adaptations. The conclusion is that the Pleistocene/Holocene boundary is not very useful in understanding the human process of early colonization and adaptation to the various ecosystems of northern South America, because a mechanism of cultural change cannot be linked to that boundary.