Ammonium content of Archean rocks of the Superior Province

Ammonium contents were determined for clastic sediments and associated volcanic rocks of the Kirkland Lake area, Abitibi greenstone- granite belt and metamorphic, migmatitic and granitic rocks of the Ear Falls-Dryden area, English River gneiss-granite belt. The NH(4) centents of Archean volcanic rocks (2700~2710m.y.) are very low (0~6 ppm) and immature argillites have also low contents of NH(4) (27~43ppm). On the other hand, a black shale from the Timiskaming Group (2100m.y.) are rich in graphite and pyrite and contain much NH4 (130ppm), providing a firm evidence of relatively abundant presence of an Archean biota compared with a sparcity of morphological record of Archean fossils. The NH(4) content of the rock mentioned above is about a third of those of the upper Proterozoic sediments and it remains to be established whether it reflects the abrupt break in the evolution of life near the Archean-Proterozoic boundary or not. A considerable amount of NH(4) is inherited by highly metamorphic pelitic gneisses and there may be a possibility for indirect prospection of early life by a study of NH(4) in highly metamorphic rocks of the early Archean. It was also found that the gneissic granitoid has much higher content of NH(4) than the post· kinematic massive granitoid

A Model for the Ultrastructure of Bone Based on Electron Microscopy of Ion-Milled Sections

The relationship between the mineral component of bone and associated collagen has been a matter of continued dispute. We use transmission electron microscopy (TEM) of cryogenically ion milled sections of fully-mineralized cortical bone to study the spatial and topological relationship between mineral and collagen. We observe that hydroxyapatite (HA) occurs largely as elongated plate-like structures which are external to and oriented parallel to the collagen fibrils. Dark field images suggest that the structures (“mineral structures”) are polycrystalline. They are approximately 5 nm thick, 70 nm wide and several hundred nm long. Using energy-dispersive X-ray analysis we show that approximately 70% of the HA occurs as mineral structures external to the fibrils. The remainder is found constrained to the gap zones. Comparative studies of other species suggest that this structural motif is ubiquitous in all vertebrates

Reconstructing the Neanderthal brain using computational anatomy

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Dating Methods of Pleistocene Deposits and Their Problems II. Uranium-Series Disequilibrium Dating

Abstract U-series dating makes use of the tendency of the short-lived daughters of 238U and 235U to be chemically separated from their parents during sedimentary processes. Ages of samples are determined either from the decay of initial excess of daughter (Daughter Excess, DE, dating) or growth of initially deficient daughter (DD) into secular equilibrium with the parent. DE dating is applicable to marine sediments where initial excesses of 230Th and 231Pa are observed. DD dating is useful on chemically precipitated CaCO3 and some biogenic carbonates. By DD dating of travertines associated with various types of geomorphic features, absolute dates for the evolution of land-forms through the Quaternary can be obtained. DD dated speleothems also yield stable isotopic records of past climate

Age determination of travertine from archaeologic sites

Where travertine has formed by slow passage of calcite saturated water on to archaeological sites, the deposits of cultural materials may be enclosed within material which is datable by a number of isotopic methods. Th-230/U-234 dating is generally applicable for travertines which are not contaminated by detritus, not too porous or permeable, and containing more than 0.1 ppm of uranium. Travertines containing 1 ppm U or more can be also dated by Pa-231/Th-230 methods. The presence of detritus may result in contamination of the sample by varying amounts of U and Th ; the latter can be recongnized by the presence of Th-232 in alpha spectra and various procedures for adjusting data to correct for Th-contamination are presented. Dates for sites ranging in age from 10.000 to greater than 350.000 yerars have been obtained for sites in Europe, Asia and North America. The use of U-234/U-238 ratio measurements, independent of knowledge of initial ratios, may now also be possible for samples of sufficiently high U content ; the ana- lysus depends on the recognition that "hot" atoms of U-234 are more readily leachable than atoms deposited at the time of formation of the sample. Leaching of the sample allows discrimination between these populations. Coupling of U-series dating with either thermoluminescence or electron spin resonance dating may extend the range of applicability.Lorsque du travertin s'est formé par le passage lent d'eau saturée en calcite sur des sites archéologiques, les dépôts de matériel industriel peuvent être inclus dans un matériau qui est datable par plusieurs méthodes isotopiques. La datation Th-230/U-234 est généralement applicable aux travertins qui ne sont pas contaminés par des détritus, ne sont pas trop poreux ou perméables, et contiennent plus de O.lppm d'uranium. Les travertins contenant 1 ppm U ou plus, peuvent aussi être datés par les méthodes Pa-231/Th- 230. La présence de détritus peut provoquer une contamination de l'échantillon par des teneurs variées de U et de Th ; ce dernier peut être reconnu par la présence de Th-232 dans des spectres alpha et il est proposé plusieurs techniques pour ajuster les données afin de corriger la contamination Th. Il a été obtenu des dates pour des sites d'Europe, d'Asie et d'Amérique du Nord variant en âge de 10.000 à plus de 350.000 ans. L'emploi de la mesure du rapport U-234/U-238, indépendamment de la connaissance des rapports initiaux, peut maintenant être aussi possible pour des échantillons d'une teneur assez élevée en U ; l'analyse dépend de la reconnaissance du fait que les atomes "chauds" de U-234 sont plus facilement lessivables que les atomes déposés au moment de la formation de l'échantillon. Le lessivage de l'échantillon permet une discrimination entre ces populations. L'association des datations par la série de U avec soit la thermoluminescence soit la datation par résonance de spin des électrons peut étendre le domaine des applications.Schwarcz Henry P. Age determination of travertine from archaeologic sites. In: Revue d'Archéométrie, n°4, 1980. pp. 101-109

Strangers In A Strange Land: Stable Isotope Evidence For Human Migration In The Dakhleh Oasis, Egypt

This study utilizes a combination of both stable oxygen and nitrogen isotope ratios to determine migration patterns for a large sample of human remains from the Kellis 2 cemetery (c. AD 250) in the Dakhleh Oasis, Egypt. Stable oxygen isotopic analysis has been used to identify potential migrants in several different populations. In this study, the data resultant from the combination of oxygen isotope ratios from bone apatite and nitrogen isotope ratios from bone collagen indicate that at least two individuals are not native to the Oasis, as shown by their lower nitrogen values and more positive oxygen isotopes, approaching values documented for residents of the Nile Valley and Nubia. The most isotopically distinctive individual is lepromatous, suggesting that he may have been exiled to the oasis from the Nile Valley. Interestingly, all individuals who have different isotope values are male, supporting the idea that males may have been involved in caravan trade between the Oasis and the Nile Valley. © 2001 Academic Press

The Ultrastructure of Bone and Its Relevance to Mechanical Properties

Bone is a biologically generated composite material comprised of two major structural components: crystals of apatite and collagen fibrils. Computational analysis of the mechanical properties of bone must make assumptions about the geometric and topological relationships between these components. Recent transmission electron microscope (TEM) studies of samples of bone prepared using ion milling methods have revealed important previously unrecognized features in the ultrastructure of bone. These studies show that most of the mineral in bone lies outside the fibrils and is organized into elongated plates 5 nanometers (nm) thick, ~80 nm wide and hundreds of nm long. These so-called mineral lamellae (MLs) are mosaics of single 5 nm-thick, 20–50 nm wide crystals bonded at their edges. MLs occur either stacked around the 50 nm-diameter collagen fibrils, or in parallel stacks of 5 or more MLs situated between fibrils. About 20% of mineral is in gap zones within the fibrils. MLs are apparently glued together into mechanically coherent stacks which break across the stack rather than delaminating. ML stacks should behave as cohesive units during bone deformation. Finite element computations of mechanical properties of bone show that the model including such features generates greater stiffness and strength than are obtained using conventional models in which most of the mineral, in the form of isolated crystals, is situated inside collagen fibrils