Browsing by Author "Camps, Pierre"
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- Magnetic fingerprint of southern Portuguese speleothems and implications for paleo- and environmental magnetismPublication . Font, Eric; Veiga-Pires, C.; Pozo, Manuel; Carvallo, Claire; De Siqueira Neto, António Carlos; Camps, Pierre; Fabre, Sébastien; Mirão, JoséEnvironmental magnetism of speleothems is still in its early stage of development. Here we report on our investigation of the environmental and paleomagnetic information that has been recorded in speleothems, and what are the factors that control its preservation and reliability. To address these issues, we used a multidisciplinary approach, including rock magnetism, petrography, scanning electron microscopy, stable carbon and oxygen isotope compositions, and major and trace element concentrations. We applied this to a set of samples from different stages of speleothem evolution: present-day dripwater (glass plates), a weathered stalactite, a fresh stalagmite, cave sediments, and terra rossa soils. These samples come from the Penico and Excentricas caves, located in two distinct aquifers of the Algarve region, South Portugal. Our results show that the main magnetic carriers of the speleothems under study are primary (detrital) and consist of maghemite (and magnetite?). Similarities in coercivity and temperature dependence of the studied set of samples suggest that iron oxides are inherited from the terra rossa soils that cap the cave and were transported to the speleothems by dripwater. Hence, they represent a regional environmental signature. Interestingly, a stable and probably detrital remanent magnetization could be isolated in the fresh stalagmite, whereas the weathered stalactite yielded chaotic magnetic directions and very low remanent intensities. We propose that these low intensities can be the result from(i) different remanence acquisition mechanisms between stalagmite and stalactite and/or (ii) iron dissolution by fungal activity. We also suggest that magnetic properties and color and the content in detrital elements in the fresh speleothem inform about environmental processes acting on the interface of rock (soil)-atmosphere, while oxygen isotope composition and alkaline-earth element concentrations inform about calcite-water interaction processes. These results provide a better understanding of how environmental information is recorded in speleothems and what the factors are that control the reliability of the paleomagnetic and paleo-environmental signal.
- Magnetic fingerprints of stalagmitesPublication . Font, Eric; Veiga-Pires, C.; Camps, Pierre; Carvallo, Claire; Neto, António; Pozo, Manuel; Mirão, JoséDating stalagmite usi ng paleomagnetic methods is still in its early stage of development. Questions still remain regarding the nature and origin of the magnetic carriers and the reliability of the natural remanent magnetization preserved within the thin carbonat ed laminations of stalagmites. Here we apply high - resolution rock - and paleo - magnetic methods on two (altered and preserved) stalagmites in order to identify the magnetic and mineralogical signatures and to assess the stability of the remanence.
- The pre-KPB interval: sedimentary record of a major Deccan Traps pulse?Publication . Font, Eric; Ponte, J.; Nédélec, Anna; Veiga-Pires, C.; Ellwood, B. B.; Camps, Pierre; Figueireido, M. O.; Silva, T. P. da; Nave, Silvia; Pozo, ManuelThe KPB crisis is one of the major biological crises that affected the Earth at Phanerozoic times. There is still an acrimonious debate on the nature and origin of this mass extinction: proponents of the idea that large bolide impacts caused most of the Phanerozoic mass extinctions are opposed to those who favoured a terrestrial origin linked to continental flood basalt eruptions of the Deccan Traps. The major limitations reside in the difficulty to date with precision the stratigraphic position of Deccan traps pulses since direct markers are still missing.