Pliocene extensional tectonics in the Eastern Central Patagonian Cordillera: geochronological constraints and new field evidence     

Yves Lagabrielle  Manuel Surez  Jacques Malavieille  Diego Morata  Felipe Espinoza  Ren C. Maury  Bruno Scalabrino  Luis Barbero  Rita de la Cruz  Eduardo Rossello  Herv Bellon 《地学学报》2007,19(6):413-424

Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera‐Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (∼2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause‐and‐effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction.  相似文献   

Preface     

Jacques Verron  Nicolas Picot 《Marine Geodesy》2015,38(3)

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Cultural and economic residential sorting of Auckland’s population, 1991–2013: an entropy approach     

Mondal  Mohana  Cameron  Michael P.  Poot  Jacques 《Journal of Geographical Systems》2021,23(2):291-330

Journal of Geographical Systems - Auckland, the largest city of New Zealand, is one of the most diverse cities in the world, with more than 40% of its population born abroad, more than 200...  相似文献   

Tidal evolution of hierarchical and inclined systems     

Alexandre C. M. Correia  Jacques Laskar  Fran?ois Farago  Gwena?l Bou�� 《Celestial Mechanics and Dynamical Astronomy》2011,111(1-2):105-130

We investigate the dynamical evolution of hierarchical three-body systems under the effect of tides, when the ratio of the orbital semi-major axes is small and the mutual inclination is relatively large (greater than 20°). Using the quadrupolar non-restricted approximation for the gravitational interactions and the viscous linear model for tides, we derive the averaged equations of motion in a vectorial formalism which is suitable to model the long-term evolution of a large variety of exoplanetary systems in very eccentric and inclined orbits. In particular, it can be used to derive constraints for stellar spin-orbit misalignment, capture in Cassini states, tidal-Kozai migration, or damping of the mutual inclination. Because our model is valid for the non-restricted problem, it can be used to study systems of identical mass or for the outer restricted problem, such as the evolution of a planet around a binary of stars. Here, we apply our model to various situations in the HD 11964, HD 80606, and HD 98800 systems.  相似文献   

Environmental degradation narratives in Madagascar: From colonial hegemonies to humanist revisionism     

Jacques Pollini 《Geoforum》2010,41(5):711-722

It is recurrently argued that political ecologists, by overlooking biophysical realities, misinterpret ecological interactions and underestimate environmental degradation. This article investigates the relevance of these critiques in the case of the Malagasy highlands. It is based on an analysis of three environmental narratives: a narrative developed by European colonists at the beginning of the century; a “modern” narrative developed since the 1980s by combining data from paleobotanists, archeologists and paleontologists; and a narrative developed more recently by political ecologists. I will show that biophysical realities were actually investigated by political ecologists in Madagascar, but that their interpretation differed from those of mainstream ecologists as a result of a different way of defining, characterizing and valuing the environment. With the aim of favoring a more comprehensive understanding of environmental degradation in Madagascar, I will propose to clarify the epistemological framework of political ecology, and to bring an objective nature back into its scope of enquiry. Far from weakening political ecology, this exercise will render the discipline more resistant to the counterattacks it has received, and more powerful for building a future that will answer to both social and environmental challenges.  相似文献   

Radiometric mapping of the Berg River estuary     

Ivan Henrico  Susan Henrico  Rikus le Roux  Jacques Bezuidenhout 《Transactions in GIS》2023,27(1):105-114

Geographic Information Systems (GIS) consists of various tools to perform spatial analyses in a wide variety of disciplines, including radiometric analysis to characterize the distribution of natural radionuclide concentrations. Recently, open-source GIS has become popular among geospatial users because it can be freely used, and powerful tools are constantly developed to enhance software capabilities. Gamma-ray spectroscopy was used to measure the concentrations of these natural radionuclides by dragging a Delta Underwater Gamma System (DUGS) among the sediment in the Berg River estuary located in Velddrif, South Africa. In this study, QGIS was used to visually illustrate and interpret the distribution of natural radionuclides, that is, potassium (K⁴⁰), thorium (Th²³²), and uranium (U²³⁸). These concentrations can be used to investigate various geographical and geological phenomena, which include sediment processes. The data were then interpreted to derive sediment characteristics. Various features of tidal estuaries were demonstrated by the results.  相似文献   

Mineralogy and geochemical behaviour during weathering of greenstone belt under tropical dry conditions in the extreme North Cameroon (Central Africa)     

Jean Pierre Nguetnkam  Fredéric Villiéras  Richard Kamga  Georges Emmanuel Ekodeck  Jacques Yvon 《Chemie der Erde / Geochemistry》2014

Mineralogy, major, trace and rare earth elements of a weathering profile developed on tertiary greenstone belt in the extreme North Cameroon are reported. The aim of which was to investigate mineralogical evolution and element mobilization and redistribution during weathering under dry tropical climate. The weathering profile consists of four main horizons: (1) a spheroidal weathering zone constituted by a corestone–shell complex, (2) a C horizon, (3) a Bw horizon and an Ah horizon. The results indicate that nontronite, a Fe-rich smectite, is the exclusive clay mineral formed in the exfoliated shells and the C horizon. It is associated with kaolinite in the upper horizons. The coexistence of these two clay minerals induced a decrease of CEC and pH which becomes neutral. The weathering index (WI) values reveal that weathering becomes more and more intensive from the corestone up to Bw horizon, which is the most weathered horizon in the weathering profile. Mass balance calculations, using Th as immobile element, indicate that Ti is quite mobile and that Al and Fe are relatively enriched at the bottom and strongly leached at the top of the profile. Alkalis and alkaline earth elements are strong leached through out the profile, except Ca which displays similar trend as Al and Fe. The same goes for LILE (Cs, Sr), TTE (Cr, Co, Ni) and HSFE (Y, Nb, Hf). In opposite, REE are depleted at the bottom and enriched in the upper horizons, with more enrichment for LREE than for HREE. It appears that weathering of greenstone belt causes a fractionation of HREE and induces a concentration of LREEs. Ce and Eu anomalies display opposite behaviour.  相似文献   

The challenge of dating early pleistocene fossil teeth by the combined uranium series–electron spin resonance method: the Venta Micena palaeontological site (Orce,Spain)     

Mathieu Duval  Christophe Falguères  Jean‐Jacques Bahain  Rainer Grün  Qingfeng Shao  Maxime Aubert  John Hellstrom  Jean‐Michel Dolo  Jordi Agusti  Bienvenido Martínez‐Navarro  Paul Palmqvist  Isidro Toro‐Moyano 《第四纪科学杂志》2011,26(6):603-615

The palaeontological site of Venta Micena (Orce, Andalusia, Spain) lies in the eastern sector of the Guadix–Baza basin, one of the best documented areas in Europe for Plio‐Pleistocene biostratigraphy. The combination of biochronological and palaeomagnetic results, combined with the radiometric data obtained for Atapuerca Sima del Elefante, indicated that the Venta Micena stratum was formed between the Jaramillo and Olduvai palaeomagnetic events, most likely between 1.22 and 1.77 Ma. Five fossil teeth from two outcrops (sites A and B) were selected to assess the potential of combined uranium series–electron spin resonance (US‐ESR) dating of Early Pleistocene sites. Although the US‐ESR results of the first outcrop showed a large scatter between the three teeth, the mean age of 1.37 ± 0.24 Ma can be considered a reasonable age estimate for Venta Micena. The mean ESR age of 0.62 ± 0.03 Ma obtained for site B seems to be a severe underestimation when compared with the independent age control. This underestimation is attributed to a relative recent U‐mobilization event that led to some U‐leaching. The results show that any ESR age calculations of old samples are extremely sensitive to variations in the measured ²³⁰Th/²³⁴U ratios in dental tissues. Although the results demonstrate that ESR can in principle be applied to Early Pleistocene sites, they also reveal the complexity of dating such old teeth. It is necessary to continue research in several directions, such as study of the behaviour of ESR signals in old teeth and understanding recent U‐mobilization processes, to improve the reliability of the combined US‐ESR dating method applied to Early Pleistocene times, a period for which the number of available numerical dating techniques is very limited. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Human choices and environmental constraints: deciphering the variability of large game procurement from Mousterian to Aurignacian times (MIS 5-3) in southwestern France     

Emmanuel Discamps  Jacques Jaubert  François Bachellerie 《Quaternary Science Reviews》2011,30(19-20):2755-2775

The evolution in the selection of prey made by past humans, especially the Neandertals and the first anatomically modern humans, has been widely debated. Between Marine Isotope Stages (MIS) 5 and 3, the accuracy of absolute dating is still insufficient to precisely correlate paleoclimatic and archaeological data. It is often difficult, therefore, to estimate to what extent changes in species procurement are correlated with either climate fluctuations or deliberate cultural choices in terms of subsistence behavior. Here, the full development of archeostratigraphy and Bayesian statistical analysis of absolute dates allows the archeological and paleoclimatic chronologies to be compared. The variability in hunted fauna is investigated using multivariate statistical analysis of quantitative faunal lists of 148 assemblages from 39 archeological sequences from MIS 5 through MIS 3. Despite significant intra-technocomplex variability, it is possible to identify major shifts in the human diet during these stages. The integration of archeological data, paleoclimatic proxies and the ecological characteristics of the different species of prey shows that the shifts in large game hunting can be explained by an adaptation of the human groups to climatic fluctuations. However, even if Middle and Early Upper Paleolithic men adapted to changes in their environment and to contrasting landscapes, they ultimately belonged to the ecosystems of the past and were limited by environmental constraints.  相似文献   

An overview of the ACE‐2 CLOUDYCOLUMN closure experiment     

J. L. Brenguier  P. Y. Chuang  Y. Fouquart  D. W. Johnson  F. Parol  Hanna Pawlowska  Jacques Pelon  Lothar Schüller  F. Schröder  J. Snider 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):815-827

CLOUDYCOLUMN is one of the 6 ACE‐2 projects which took place in June‐July 1997, between Portugal and the Canary Islands. It was specifically dedicated to the study of changes of cloud radiative properties resulting from changes in the properties of those aerosols which act as cloud condensation nuclei. This process is also refered to as the aerosol indirect effect on climate. CLOUDYCOLUMN is focused on the contribution of stratocumulus clouds to that process. In addition to the basic aerosol measurements performed at the ground stations of the ACE‐2 project, 5 instrumented aircraft carried out in situ characterization of aerosol physical, chemical and nucleation properties and cloud dynamical and microphysical properties. Cloud radiative properties were also measured remotely with radiometers and a lidar. 11 case studies have been documented, from pure marine to significantly polluted air masses. The simultaneity of the measurements with the multi‐aircraft approach provides a unique data set for closure experiments on the aerosol indirect effect. In particular CLOUDYCOLUMN provided the 1st experimental evidence of the existence of the indirect effect in boundary layer clouds forming in polluted continental outbreacks. This paper describes the objectives of the project, the instrumental setup and the sampling strategy. Preliminary results published in additional papers are briefly summarized.  相似文献