Tephrochronology

Tephrochronology is the use of primary, characterized tephras or cryptotephras as chronostratigraphic marker beds to connect and synchronize geological, paleoenvironmental, or archaeological sequences or events, or soils/paleosols, and, uniquely, to transfer relative or numerical ages or dates to them using stratigraphic and age information together with mineralogical and geochemical compositional data, especially from individual glass-shard analyses, obtained for the tephra/cryptotephra deposits. To function as an age-equivalent correlation and chronostratigraphic dating tool, tephrochronology may be undertaken in three steps: (i) mapping and describing tephras and determining their stratigraphic relationships, (ii) characterizing tephras or cryptotephras in the laboratory, and (iii) dating them using a wide range of geochronological methods. Tephrochronology is also an important tool in volcanology, informing studies on volcanic petrology, volcano eruption histories and hazards, and volcano-climate forcing. Although limitations and challenges remain, multidisciplinary applications of tephrochronology continue to grow markedly

Geometry and field theory in multi-fractional spacetime

We construct a theory of fields living on continuous geometries with fractional Hausdorff and spectral dimensions, focussing on a flat background analogous to Minkowski spacetime. After reviewing the properties of fractional spaces with fixed dimension, presented in a companion paper, we generalize to a multi-fractional scenario inspired by multi-fractal geometry, where the dimension changes with the scale. This is related to the renormalization group properties of fractional field theories, illustrated by the example of a scalar field. Depending on the symmetries of the Lagrangian, one can define two models. In one of them, the effective dimension flows from 2 in the ultraviolet (UV) and geometry constrains the infrared limit to be four-dimensional. At the UV critical value, the model is rendered power-counting renormalizable. However, this is not the most fundamental regime. Compelling arguments of fractal geometry require an extension of the fractional action measure to complex order. In doing so, we obtain a hierarchy of scales characterizing different geometric regimes. At very small scales, discrete symmetries emerge and the notion of a continuous spacetime begins to blur, until one reaches a fundamental scale and an ultra-microscopic fractal structure. This fine hierarchy of geometries has implications for non-commutative theories and discrete quantum gravity. In the latter case, the present model can be viewed as a top-down realization of a quantum-discrete to classical-continuum transition.Comment: 1+82 pages, 1 figure, 2 tables. v2-3: discussions clarified and improved (especially section 4.5), typos corrected, references added; v4: further typos correcte

Physical Methods for the Preparation of Hybrid Nanocomposite Polymer Latex Particles

In this chapter, we will highlight conceptual physical approaches towards the fabrication of nanocomposite polymer latexes in which each individual latex particle contains one or more "hard" nanoparticles, such as clays, silicates, titanates, or other metal(oxides). By "physical approaches" we mean that the "hard" nanoparticles are added as pre-existing entities, and are not synthesized in situ as part of the nanocomposite polymer latex fabrication process. We will narrow our discussion to focus on physical methods that rely on the assembly of nanoparticles onto the latex particles after the latex particles have been formed, or its reciprocal analogue, the adhesion of polymer onto an inorganic nanoparticle. First, will discuss the phenomenon of heterocoagulation and its various driving forces, such as electrostatic interactions, the hydrophobic effect, and secondary molecular interactions. We will then address methods that involve assembly of nanoparticles onto or around the more liquid precursors (i.e., swollen/growing latex particles or monomer droplets). We will focus on the phenomenon of Pickering stabilization. We will then discuss features of particle interaction with soft interfaces, and see how the adhesion of particles onto emulsion droplets can be applied in suspension, miniemulsion, and emulsion polymerization. Finally, we will very briefly mention some interesting methods that make use of interface-driven templating for making well-defined assembled clusters and supracolloidal structures

Correspondence between glass-FT and ¹⁴C ages of silicic pyroclastic flow deposits sourced from Maninjau caldera, west-central Sumatra

Paroxysmal pyroclastic flow deposits sourced from Maninjau caldera in west-central Sumatra are dated at 50+/-3 ka (n=3) using the isothermal plateau and diameter corrected fission-track (ITPFT and DCFT, respectively) techniques on glass shard constituents. In addition, charcoal obtained from tall trees in position of growth within the paroxysmal flow deposit on the upper flanks for the caldera are also dated at 52.3+/-2 C-14 ka (n=2) and 51.1+/-3.2 C-14 ka (n-1) using an acid-base, wet oxidation, stepped combustion (ABOX-SC) and standard acid-base-acid (ABA) C-14 techniques, respectively. The close correspondence in C-14 ages of charcoal sample splits analysed at two laboratories (Australian National University, Australia and Waikato University. New Zealand) verifies the reliability of these C-14 techniques up to at least 50 ka.Based on concordant ages derived from glass-FT and C-14 techniques, an age of 52+/-3 ka is assigned to the latest silicic eruptive activity at Maninjau caldera. This chronology is further confirmed by the occurrence of a silicic tephra bed that closely underlies paroxysmal Maninjau deposits at two sections and is correlated with Youngest (75 ka) Toba Tephra (YTT) erupted from Toba caldera in north-central Sumatra. This study not only provides a much needed regional chronological reference point for Quaternary deposits in west-central Sumatra but also extends the minimum age range of the glass-FT technique from 75 ka down to c. 50 ka that is now for the first time within the extended maximum age range of the C-14 technique. (C) 2004 Elsevier B.V. All rights reserved.</p

Correspondence between glass-FT and ¹⁴C ages of silicic pyroclastic flow deposits sourced from Maninjau caldera, west-central Sumatra

Paroxysmal pyroclastic flow deposits sourced from Maninjau caldera in west-central Sumatra are dated at 50+/-3 ka (n=3) using the isothermal plateau and diameter corrected fission-track (ITPFT and DCFT, respectively) techniques on glass shard constituents. In addition, charcoal obtained from tall trees in position of growth within the paroxysmal flow deposit on the upper flanks for the caldera are also dated at 52.3+/-2 C-14 ka (n=2) and 51.1+/-3.2 C-14 ka (n-1) using an acid-base, wet oxidation, stepped combustion (ABOX-SC) and standard acid-base-acid (ABA) C-14 techniques, respectively. The close correspondence in C-14 ages of charcoal sample splits analysed at two laboratories (Australian National University, Australia and Waikato University. New Zealand) verifies the reliability of these C-14 techniques up to at least 50 ka.Based on concordant ages derived from glass-FT and C-14 techniques, an age of 52+/-3 ka is assigned to the latest silicic eruptive activity at Maninjau caldera. This chronology is further confirmed by the occurrence of a silicic tephra bed that closely underlies paroxysmal Maninjau deposits at two sections and is correlated with Youngest (75 ka) Toba Tephra (YTT) erupted from Toba caldera in north-central Sumatra. This study not only provides a much needed regional chronological reference point for Quaternary deposits in west-central Sumatra but also extends the minimum age range of the glass-FT technique from 75 ka down to c. 50 ka that is now for the first time within the extended maximum age range of the C-14 technique. (C) 2004 Elsevier B.V. All rights reserved.</p