Vegetation and climate near Lago Llanquihue in the Chilean Lake District between 20200 and 9500 14C yr BP     

Patricio I. Moreno 《第四纪科学杂志》1997,12(6):485-500

Radiocarbon-dated pollen records of two adjacent sediment cores from Canal de la Puntilla (40°57′09″S, 72°54′18″W) in the Chilean Lake District reveal that a sparsely vegetated landscape prevailed during the portion of the Last Glacial Maximum between 20200 and about 14800 ¹⁴C yr BP. Dominating the vegetation was Nothofagus, Gramineae and Compositae, along with taxa commonly found today above the Andean treeline (Perezia-type, Valeriana) and in Magellanic Moorlands (Donatia, Astelia). Nothofagus expanded between 20200 and 15800 ¹⁴C yr BP, interrupted by a reversal at 19200 ¹⁴C yr BP and followed by a prominent increase in Gramineae pollen between 15800 and about 14800 ¹⁴C yr BP. A major increase in Nothofagus started at about 14800 ¹⁴C yr BP, followed by an abrupt expansion of thermophilous Valdivian/North Patagonian Rain Forest taxa (Myrtaceae, Lomatia/Gevuina, Hydrangea, etc.) at about 14000 ¹⁴C yr BP. An opening of the rain forest and an expansion of Podocarpus nubigena, Misodendrum, and Maytenus disticha-type subsequently occurred between 11000 and 10000 ¹⁴C yr BP. These results suggest that mean annual temperature was 6–7°C colder than at present, with twice the modern annual precipitation between 20200 and 14000 ¹⁴C yr BP, implying a northward shift and intensification of the westerlies storm-tracks. Slight climate warming occurred between 20200 and 15800 ¹⁴C yr BP, featuring cooling reversals at 19200 ¹⁴C yr BP, and later at 15800 ¹⁴C yr BP. The warming of the last termination started at about 14800 ¹⁴C yr BP, and reached a total temperature rise of ≥5°C by 12400 ¹⁴C yr BP, followed by cooling between 11000 and 10000 ¹⁴C yr BP. © 1997 John Wiley & Sons, Ltd.  相似文献   

Generalized algorithms for particle motion and collision with streambeds     

Patricio A.Moreno-Casas  Fabian A. Bombardelli  Juan Pablo Toro 《国际泥沙研究》2019,34(4):295-306

Recent theoretical and numerical models for the motion of saltating particles close to stream beds are constituted of three sub-models: a) a set of equations describing the particle “free flight”, b) a sub-model to calculate the post-collision particle velocity, and c) a mathematical representation of the bed roughness. In this paper, a comprehensive three-dimensional (3-D), theoretical/numerical model for bedload motion at large Reynolds numbers is presented. By using geometric considerations and stochastic parameters to characterize collisions with the wall, five new sub-models for representation of bed roughness are, for the first time to the best of our knowledge, proposed and implemented. The emphasis of this paper is on the particle model, for which Basset, Magnus, drag, submerged weight, virtual mass, and lift forces are included. For the range of particle sizes (sands) analyzed herein, it is found that the stream-wise contribution of the Basset force, compared to other forces, may be as large as 60%. Whereas in the wall-normal direction, the Basset force is equally important as the drag force, and it is exceeded only by the submerged weight. It is also found that the best agreement between numerical and experimental results in terms of jump length, jump height, and stream-wise particle velocity is achieved for restitution and friction coefficients of 0.65 and 0.1, respectively. Important conclusions are obtained regarding the lack of realistic prediction with available “roughness” models with small ranges of angles.  相似文献   

Estimation of the seismic wavelet through homomorphic deconvolution and well log data: application on well-to-seismic tie procedure     

Isadora A.S. de Macedo  Jose Jadsom S. de Figueiredo  Matias C. de Sousa  Murillo J.S. Nascimento 《Geophysical Prospecting》2020,68(4):1328-1340

Wavelet estimation and well-tie procedures are important tasks in seismic processing and interpretation. Deconvolutional statistical methods to estimate the proper wavelet, in general, are based on the assumptions of the classical convolutional model, which implies a random process reflectivity and a minimum-phase wavelet. The homomorphic deconvolution, however, does not take these premises into account. In this work, we propose an approach to estimate the seismic wavelet using the advantages of the homomorphic deconvolution and the deterministic estimation of the wavelet, which uses both seismic and well log data. The feasibility of this approach is verified on well-to-seismic tie from a real data set from Viking Graben Field, North Sea, Norway. The results show that the wavelet estimated through this methodology produced a higher quality well tie when compared to methods of estimation of the wavelet that consider the classical assumptions of the convolutional model.  相似文献   

Hydrothermal fluid flow associated to the extensional evolution of the Adriatic rifted margin: Insights from the pre- to post-rift sedimentary sequence (SE Switzerland,N ITALY)     

Nicolò Incerpi  Luca Martire  Gianreto Manatschal  Stefano M. Bernasconi  Axel Gerdes  György Czuppon  László Palcsu  Garry D. Karner  Christopher A. Johnson  Patricio H. Figueredo 《Basin Research》2020,32(1):91-115

This paper investigates the hydrothermal fluid circulation that was linked to the extensional evolution of the Adriatic rifted margin during the Jurassic opening of the Alpine Tethys. Remnants of this rifted margin are spectacularly preserved in SE Switzerland and N Italy. Five study areas were chosen ranging from the former proximal to the most distal part of the margin. We demonstrate an intimate link between Jurassic extensional tectonics and fluid activity affecting the pre- to early post-rift sedimentary sequences. Nature, composition and origin of fluids are constrained by a multidisciplinary approach based on field observations and including geochemical (O-C, Sr, He isotopes, U-Pb datings, fluid inclusion microthermometry) and petrological methods. Several fluid-related diagenetic products and processes such as dolomitization, veining, hydraulic brecciation, and silicification can be recognized. It appears that different paleogeographic settings and different stratigraphic levels document distinct phases of fluid activity. The fluids reached temperatures of up to 150°C near paleo-seafloor. They were enriched in ¹⁸O, had high ⁸⁷Sr/⁸⁶Sr and low ³He/⁴He ratios, documenting a strong interaction between seawater and a granitic basement. Many lines of evidence point to the occurrence of over-pressured fluids and long-lasting fluid circulation due to fault-valve mechanisms and high thermal gradients. Two main stages with different fluid chemistry can be recognized: (1) a carbonate-rich stage that developed during the stretching phases and was linked to high-angle normal faulting, and (2) a silica-rich stage occurring during late rift exhumation of crustal and mantle rocks in the distal domains in the presence of detachment faults and high thermal gradients. This paper provides, for the first time, a large and robust characterization of fluid–rock interactions occurring during rifting along an almost complete section across a magma-poor rifted margin.  相似文献