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21.
Luminescence dating of the top of a deep water core from the NESTOR site near the Hellenic Trench,east Mediterranean Sea 总被引:1,自引:0,他引:1
George S. Polymeris George Kitis Anastasios K. Liolios Anastasios Sakalis Konstantin Zioutas Efstratios G. Anassontzis Nestor C. Tsirliganis 《Quaternary Geochronology》2009,4(1):68-81
In the present study, the uppermost 3 cm of muddy, seabed sediment was collected from a deep-sea sediment core, drilled from a water depth of 4 km, near the deepest site of the Mediterranean Sea, outside Pylos, Greece. The core was divided into 7 layer samples, each 3–4 mm thick, in order to get an independent age assessment for each one using luminescence dating; from polymineral coarse grains in the range 30–60 μm. Between 11 and 22 aliquots were measured for each sample using the optically stimulated luminescence, single-aliquot regenerative-dose analysis. The estimated mean equivalent dose values had an uncertainty less than 3% and resulted in optical ages ranging from 3.5 to approximately 5 ka, with uncertainties lying between 5.5 and 7.4%. Multiple-aliquot, thermoluminescence-based, additive-dose, total bleaching approach provided equivalent doses with typical errors of 10–15% and ages in the range of 3.6 and 9.4 ka, with uncertainties up to 17%. Single-aliquot optical ages are shown to be relatively successful, due to their consistency with AMS 14C radiocarbon ages, obtained from Planktonic foraminifera from the same core. Luminescence dates for the topmost 1.5 cm indicate a substantial mix and post burial disturbance of the surface sediment. Below the topmost 1.5 cm, both luminescent approaches indicate ages which increase smoothly with depth. The concordant OSL and TL age estimates for the sample O5, in conjunction with specific luminescence properties and its major-element geochemical chemistry content, suggest that it was heated during the Santorini volcanic eruption. Deposition rates of 8.6–18.9 cm over 10 ka below the sample O5, provided by optical ages, exhibit an excellent level of agreement with the accumulation rate of 7–18 cm over 10 ka at the sea bottom, already reported for the site under study. 相似文献
22.
Nestor Vegas Seta Naba Jean Luc Bouchez Mark Jessell 《International Journal of Earth Sciences》2008,97(6):1165-1180
The Fada N′Gourma area in Burkina Faso is underlain by Paleoproterozoic rocks that make the northeastern West-African Craton.
This region is composed of NE-trending volcano-sedimentary belts and foliated tonalites, affected by several shear zones.
A generation of younger, ∼2100 Ma-old, non-foliated biotite-bearing granites intrudes the former rock units. We have investigated
the younger granite pluton of Kouare that was previously considered as forming a single body with the pluton of Satenga to
the west, a pluton which likely belongs to the ∼20 Ma more recent Tenkodogo-Yamba batholith. Magnetic fabric measurements
have been combined with microstructural observations and the analysis of field and aeromagnetic data. The granite encloses
angular enclaves of the host tonalites. Magmatic microstructures are preserved inside the pluton and solid-state, high-temperature
deformation features are ubiquitous at its periphery. The presence of steeply plunging lineations in the pluton of Kouare
and its adjacent host-rocks suggests that large volumes of granitic magmas became crystallized while they were ascending through
the crust that was softened and steepened close to the contact. Around Kouare, the foliation in the host tonalites conforms
with a map-scale, Z-shaped fold in between NNE-trending shear zones, implying a bulk clockwise rotation of the material contained
in-between the shear zones, including the emplacing pluton. Regionally, the Fada N′Gourma area is concluded to result from
NW-shortening associated with transcurrent shearing and vertical transfer of granitic magmas. This study concludes that the
∼2200 Myears old juvenile crust of Burkina Faso was brittle before the intrusion of the biotite-granites, became softened
close to them and that gravity-driven and regional scale wrench tectonics were active together. 相似文献
23.
Pierre-Henri Blard Jérôme Lave Kenneth A. Farley Victor Ramirez Nestor Jimenez Léo C.P. Martin Julien Charreau Bouchaïb Tibari Michel Fornari 《Quaternary Research》2014
This work presents the first reconstruction of late Pleistocene glacier fluctuations on Uturuncu volcano, in the Southern Tropical Andes. Cosmogenic 3He dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka. Despite important scatter in the exposure ages on the oldest moraines, probably resulting from pre-exposure, these 3He data constrain the timing of the moraine deposits and subsequent glacier recessions: the Uturuncu glacier may have reached its maximum extent much before the global LGM, maybe as early as 65 ka, with an equilibrium line altitude (ELA) at 5280 m. Then, the glacier remained close to its maximum position, with a main stillstand identified around 40 ka, and another one between 35 and 17 ka, followed by a limited recession at 17 ka. Then, another glacial stillstand is identified upstream during the late glacial period, probably between 16 and 14 ka, with an ELA standing at 5350 m. This stillstand is synchronous with the paleolake Tauca highstand. This result indicates that this regionally wet and cold episode, during the Heinrich 1 event, also impacted the Southern Altiplano. The ELA rose above 5450 m after 14 ka, synchronously with the Bolling–Allerod. 相似文献