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Soil testing [permeability] --- Soil testing [shear strength] --- Soil testing [granulometry]

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Les sédiments de lacs de cratère sont des archives paléoclimatiques, contenant des traceurs de l'altération des roches et sols voisins qui peuvent fournir des informations sur les variations des précipitations des derniers milliers d'années. Au Mexique central, les pluies sont influencées par divers phénomènes atmosphériques, pas encore complètement compris aujourd'hui, et qui vont pourtant être modifiés par les changements climatiques et avoir un effet météorologique important à divers endroits de la planète. Deux carottes courtes de sédiments de lacs de cratère du Mexique central ont été prélevées et analysées par différentes méthodes sédimentologiques, géochimiques et minéralogiques afin de trouver des traceurs d'altération: susceptibilité magnétique, SCOPIX, XRF Core Scanner, pertes au feu, rapport C/N, granulométrie laser, XRF discrète et DRX. Dans le Lac Los Espinos, différents traceurs semblent indiquer deux périodes marquées par une pluviosité plus élevée, entre 10 et 15 cm et entre 33 et 37 cm de profondeur, ainsi qu'une période de pluviosité plus faible, entre 15 et 30 cm. Des profondeurs précises de changement de pluviosité n'ont pas pu être identifiées dans les sédiments du Lac Tacámbaro mais les traceurs géochimiques pourraient montrer des successions rapides de pluviosité plus forte et plus faible jusqu'à 56 cm, où les variations diminuent. Ces hypothèses pourront être confirmées ou infirmées à l'aide de données météorologiques des stations voisines et des données de datation en cours de traitement, si leur résolution temporelle le permet. Les traceurs d'altération avérés pourraient alors être utilisés pour étudier les changements climatiques passés avec de plus longues carottes. Crater lake sediments are paleoclimatic archives, containing proxies of the weathering of nearby rocks and soils that can provide information about changes in precipitation during the last thousands of years.
In Central Mexico, rainfall is influenced by various atmospheric phenomena which are not yet fully understood, but which will be affected by climate change and have meteorological impacts on many locations around the globe.
Two short cores of sediments from Central Mexican crater lakes were collected and analysed by different sedimentological, geochemical and mineralogical methods, looking for weathering proxies: magnetic susceptibility, SCOPIX, XRF Core Scanner, loss on ignition, C/N ratio, laser granulometry, discrete XRF and DRX.
In Lake Los Espinos, geochemical proxies linked to the detritic elements appear to point to two periods, between 10 and 15 cm and between 33 and 37 cm, where precipitation was higher, and to another, between 15 and 30 cm, where it was lower.
Although it has not been possible to identify precise depths providing evidence of precipitation change in Lake Tacámbaro sediments, geochemical proxies may show rapid successions of higher and lower precipitation up to 56 cm, where the pace of variations declines. It will be possible to confirm or disprove these assumptions based both on the dating data currently being processed (their temporal resolution allowing) and on meteorological data from the neighbouring stations. Proven weathering proxies could then be used to study past climate changes on longer cores. Los sedimentos de los lagos cratéricos representan un archivo paleoclimático rico en trazadores de la meteorización de rocas y suelos locales que pueden dar información sobre las variaciones en las precipitaciones de los últimos miles de años. En el centro de México, las lluvias están influenciadas por diversos fenómenos atmosféricos, aún no completamente entendidos hoy, pero que sin embargo serán modificados por el cambio climático y tendrán un efecto meteorológico significativo en muchas zonas del planeta. Efectuamos nuestros análisis sobre dos núcleos de sedimentos extraídos de lagos cratéricos en el centro de México, utilizando diferentes métodos sedimentológicos, geoquímicos y mineralógicos para encontrar trazadores de meteorización: susceptibilidad magnética, SCOPIX, XRF Core Scanner, pérdidas por ignición, relación C/N, granulometría láser, XRF discreto y DRX. En el Lago Los Espinos, los trazadores geoquímicos vinculados a elementos detríticos parecen indicar dos períodos con mayor precipitación entre 10 y 15 cm y entre 33 y 37 cm y otro, con menor precipitación, entre 15 y 30 cm. No se pudieron identificar profundidades precisas de cambio de lluvia en los sedimentos del Lago Tacámbaro, aunque los trazadores geoquímicos muestran sucesiones rápidas de precipitaciones más altas y más bajas hasta 56 cm, donde las variaciones disminuyen. Estas hipótesis se podrán confirmar o invalidar con los datos de datación que se está procesando, si su resolución temporal lo permita, así como los datos meteorológicos de las estaciones vecinas. Los trazadores de meteorización comprobados podrían pues utilizarse para estudiar cambios climáticos pasados con núcleos más largos.

Paléoclimatologie --- Tacámbaro --- Los Espinos --- XRF Core Scanner --- SCOPIX --- DRX --- Granulométrie --- Précipitations --- Traceurs géochimiques --- Altération --- Paleoclimatology --- Tacámbaro --- Los Espinos --- Precipitation --- XRF Core Scanner --- SCOPIX --- XRD --- Granulometry --- Geochemical proxies --- Weathering --- Paleoclimatología --- Tacámbaro --- Los Espinos --- Precipitación --- XRF Core Scanner --- SCOPIX --- DRX --- Granulometría --- Trazadores geoquímicos --- Meteorización --- Physique, chimie, mathématiques & sciences de la terre > Sciences de la terre & géographie physique

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The principal aim of this book is to provide a wide range of information and a useful reference for researchers interested to investigate heavy mineral assemblages in different geological settings and for a variety of purposes. The methodological developments achieved in recent years for the identification of heavy minerals in a wide grain-size range are illustrated. All factors that affect heavy mineral concentration and relative proportions, including hydraulic sorting, mechanical abrasion, chemical weathering, and post-depositional dissolution, and all factors able to introduce analytical, environmental, or diagenetic bias are thoroughly addressed. A proper integration of multiple techniques including bulk sediment, multi-mineral, and single-mineral methods are discussed by renowned authors in their invited contributions.

Research & information: general --- heavy minerals --- correlation --- North Sea --- Jurassic --- Triassic --- Carboniferous --- Devonian --- relative and absolute abundances --- sampling strategy --- size-window for analysis --- heavy mineral point-counting --- provenance and plate-tectonic setting --- chemical weathering --- hydraulic sorting --- recycling --- diagenesis --- sediment --- provenance --- statistics --- zircon --- point counting --- petrography --- mineral grains composition --- surface textures --- sources --- WNW Portuguese Continental Margin --- Raman spectroscopy --- sedimentary provenance --- automatization --- heavy mineral --- Pliocene --- the Changjiang Delta --- amphibole --- surface texture --- garnet --- epidote --- pyroxene --- provenance tracers --- varietal studies --- mineral chemistry --- semi-automated Raman counting --- Ladakh-Kohistan arcs --- Himalaya --- Nanga Parbat --- Karakorum --- Indus river --- amphiboles --- tremolite --- actinolite --- provenance analysis --- tectonic versus climatic control --- early-middle Pleistocene transition --- Yellow River terraces --- Lanzhou (northern China) --- sieving of fine silt --- fallacy of laser granulometry --- benthic foraminifera --- Ganga-Brahmaputra river system --- Bay of Bengal --- Himalayan orogen --- bulk-sediment petrography --- bulk-sediment geochemistry --- selective entrainment --- suspension sorting --- chemical indices of weathering --- sediment budgets --- Brahmaputra River --- Ganga River --- handbook for laboratory procedures --- nontoxic heavy liquids --- wet sieving of silt --- zircon separation --- heavy-mineral mounts --- heavy minerals --- correlation --- North Sea --- Jurassic --- Triassic --- Carboniferous --- Devonian --- relative and absolute abundances --- sampling strategy --- size-window for analysis --- heavy mineral point-counting --- provenance and plate-tectonic setting --- chemical weathering --- hydraulic sorting --- recycling --- diagenesis --- sediment --- provenance --- statistics --- zircon --- point counting --- petrography --- mineral grains composition --- surface textures --- sources --- WNW Portuguese Continental Margin --- Raman spectroscopy --- sedimentary provenance --- automatization --- heavy mineral --- Pliocene --- the Changjiang Delta --- amphibole --- surface texture --- garnet --- epidote --- pyroxene --- provenance tracers --- varietal studies --- mineral chemistry --- semi-automated Raman counting --- Ladakh-Kohistan arcs --- Himalaya --- Nanga Parbat --- Karakorum --- Indus river --- amphiboles --- tremolite --- actinolite --- provenance analysis --- tectonic versus climatic control --- early-middle Pleistocene transition --- Yellow River terraces --- Lanzhou (northern China) --- sieving of fine silt --- fallacy of laser granulometry --- benthic foraminifera --- Ganga-Brahmaputra river system --- Bay of Bengal --- Himalayan orogen --- bulk-sediment petrography --- bulk-sediment geochemistry --- selective entrainment --- suspension sorting --- chemical indices of weathering --- sediment budgets --- Brahmaputra River --- Ganga River --- handbook for laboratory procedures --- nontoxic heavy liquids --- wet sieving of silt --- zircon separation --- heavy-mineral mounts