Search results for "GC"
showing 10 items of 606 documents
Growth of stylolite teeth patterns depending on normal stress and finite compaction
2007
Abstract Stylolites are spectacular rough dissolution surfaces that are found in many rock types. They are formed during a slow irreversible deformation in sedimentary rocks and therefore participate to the dissipation of tectonic stresses in the Earth's upper crust. Despite many studies, their genesis is still debated, particularly the time scales of their formation and the relationship between this time and their morphology. We developed a new discrete simulation technique to explore the dynamic growth of the stylolite roughness, starting from an initially flat dissolution surface. We demonstrate that the typical steep stylolite teeth geometry can accurately be modelled and reproduce natu…
Rare earth element and neodymium isotope tracing of sedimentary rock weathering
2020
Chemical weathering plays an important role in sequestering atmospheric CO2, but its potential influence on global climate over geological timescales remains debated. To some extent, this uncertainty arises from the difficulty in separating the respective contribution of sedimentary and crystalline silicate rocks to past weathering rates in the geological record; two types of rocks having presumably different impact on the long-term carbon cycle. In this study, we investigate the use of rare earth element (REE) and neodymium isotopes (εNd) in leached iron oxide fractions of river sediments for tracing the origin of weathered rocks on continents. A new index, called ‘concavity index’ (CI), i…
Identification of processes that control the stable isotope composition of rainwater in the humid tropical West-Central Africa.
2020
12 pages; International audience; This study interprets 11 years (2006 to 2016) and 6 months (March to August in 2017) of respectively monthly and daily isotopic (δD and δ18O) monitoring of rain at Douala (Cameroon), a humid tropical station in Western Africa. The main scope is to analyze the climate controls on precipitation isotopes at different timescales. Firstly, we examine the annual cycles of δ18O. Over the 11 years of survey, the annual cycle exhibits a W shape that is quite reproducible from year to year, with two minima in spring and autumn periods. Based on back trajectory calculations and remote sensing observations of water vapor isotopic composition, we show that the observed …
In situ carbon and oxygen isotopes measurements in carbonates by fiber coupled laser diode-induced calcination: A step towards field isotopic charact…
2021
International audience; Natural stable isotopes ratios (δ13Ccarb and δ18Ocarb) of carbonates archived in the geological record are routinely used to reconstruct local and global paleo temperatures and the secular evolution of the biogeochemical carbon cycle. The state-of-the-art technique, employed since the mid 20th century, to measure these isotopic ratios starts with field sampling followed by several steps of physical and chemical laboratory preparation including: (i) microdrilling and/or sawing and crushing, (ii) CO2 release by wet acid digestion, (iii) gas equilibration, purification and transfer, before (iv) gas phase IRMS measurements. While these steps are time and resource consumi…
Summer air temperature, reconstructions from the last glacial stage based on rodents from the site Taillis-des-Coteaux (Vienne), Western France.
2014
AbstractThe oxygen isotope composition of phosphate from tooth enamel of rodents (δ18Op) constitutes a valuable proxy to reconstruct past air temperatures in continental environments. This method has been applied to rodent dental remains from three genera, Arvicola sp., Microtus sp. and Dicrostonyx sp., coming from Taillis-des-Coteaux, Vienne, France. This archaeological site contains an exceptionally preserved sedimentary sequence spanning almost the whole Upper Palaeolithic, including seven stratigraphic layers dated from 35 to 17 cal ka BP. The abundant presence of rodent remains offers the opportunity to quantify the climatic fluctuations coeval of the various stages of human occupation…
The history and impacts of farming activities in south Greenland: an insight from lake deposits.
2013
International audience; Agriculture in southern Greenland has a two-phase history: with the Norse, who first settled and farmed the region between 985ad and circa 1450ad, and with the recent reintroduction of sheep farming (1920ad to the present). The agricultural sector in Greenland is expected to grow over the next century as anticipated climate warming extends the length of the growing season and increases productivity. This article presents a synthesis of results from a well-dated 1500-year lake sediment record from Lake Igaliku, south Greenland (61°00′N, 45°26′W, 15m asl) that demonstrates the relative impacts of modern and Norse agricultural activities. Pollen, non-pollen palynomorphs…
Evidence of aerial volcanic activity during the Valanginian along the northern Tethys margin.
2009
7 pages; International audience; Stratigraphic measurement and sampling on three sections (Vergol, La Charce, and Montclus) through Valanginian deposits from the Vocontian Basin (southeastern France) reveals the occurrence of centimetre thick ochre-coloured layers, which can be correlated from one section to another. At least twelve of these are identified in sediments dated from the Pertransiens to Furcillata ammonite Zones. These horizons appear similar to previously described Oxfordian and Aptian bentonites, also from the Vocontian Basin. Clay-mineralogical and geochemical data are similar in the Valanginian ochre horizons and their enclosing marls except in one of these that shows a cla…
New results in ancient Maya rituals researches: The study of human painted bones fragments from Calakmul archaeological site (Mexico)
2020
Abstract The funeral chambers of the ancient city of Calakmul (Mexico) and the individuals who were buried in them have brought in recent decades new knowledge about the beliefs and funeral customs of the pre-Hispanic Maya. Tombs and bodies were prepared as part of the rituals that should favor the return of ch'ulel to the Underworld, known as Xibalba by the ancient Maya. The ch'ulel is one of the two anemic entities that inhabit the individual, equivalent to our concept of the soul. Bodies preparation included coloured scented body ointments application, with a deep symbolic connotation and probably also a conservative purpose. The aim of this research was to characterize pigments and bind…
Intra-skeletal variability in trace elemental content of Precolumbian Chupicuaro human bones: the record of post-mortem alteration and a tool for pal…
2011
14 pages; International audience; This study applies an intra-skeletal sampling strategy to examine post-mortem alteration of archaeological human bone from west Mexico, and to reconstruct ancient diet. Human bone from the Chupicuaro culture (Mexico, Preclassic period) constitutes an ideal material with which to examine subsistence strategies because the specific hydrothermal environment in which the population lived would have provided certain food components (hydrothermal waters and carbonates) with distinct signature in Ca, Mg, F, Li, Sr, Mn, V and U values. Four to ten samples were taken from the long bones of six skeletons. Bone trace element content (Ca, P, F, Mn, Mg, Na, Li, V, Zn, R…
Tracking archaeological and historical mines using mineral prospectivity mapping.
2014
13 pages; International audience; The present study proposes a technological transfer from modern mining prospection to the field of archaeology, providing a methodology to facilitate the discovery of ancient mining sites. This method takes advantage of the thousands of geochemical analyses of streambed sediments, performed by national geological surveys to inventory mineral substances. In order to delineate geochemical anomalies, the datasets are treated following two different approaches: Exploratory Data Analysis and a fractal-based method often recognised as more powerful. Mineral prospectivity maps are then obtained by combining the results with a geographical information system. The s…