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101.
Joel E. Saylor Brian K. Horton Junsheng Nie Jaime Corredor Andrés Mora 《Basin Research》2011,23(4):377-402
This paper addresses foreland basin fragmentation through integrated detrital zircon U–Pb geochronology, sandstone petrography, facies analysis and palaeocurrent measurements from a Mesozoic–Cenozoic clastic succession preserved in the northern Andean retroarc fold‐thrust belt. Situated along the axis of the Eastern Cordillera of Colombia, the Floresta basin first received sediment from the eastern craton (Guyana shield) in the Cretaceous–early Palaeocene and then from the western magmatic arc (Central Cordillera) starting in the mid‐Palaeocene. The upper‐crustal magmatic arc was replaced by a metamorphic basement source in the middle Eocene. This, in turn, was replaced by an upper‐crustal fold‐thrust belt source in the late Eocene which persisted until Oligocene truncation of the Cenozoic section by the eastward advancing thrust front. Sedimentary facies analysis indicates minimal changes in depositional environments from shallow marine to low‐gradient fluvial and estuarine deposits. These same environments are recorded in coeval strata across the Eastern Cordillera. Throughout the Palaeogene, palaeocurrent and sediment provenance data point to a uniform western or southwestern sediment source. These data show that the Floresta basin existed as part of a laterally extensive, unbroken foreland basin connected with the proximal western (Magdalena Valley) basin from mid‐Paleocene to late Eocene time when it was isolated by uplift of the western flank of the Eastern Cordillera. The Floresta basin was also connected with the distal eastern (Llanos) basin from the Cretaceous until its late Oligocene truncation by the advancing thrust front. 相似文献
102.
M. Teresa Ram��rez-Herrera Vladimir Kostoglodov Jaime Urrutia-Fucugauchi 《Pure and Applied Geophysics》2011,168(8-9):1415-1433
Holocene and Pleistocene tectonic deformation of the coast in the Mexico subudction margin is recorded by geomorphic and stratigraphic markers. We document the spatial and temporal variability of active deformation on the coastal Mexican subduction margin. Pleistocene uplift rates are estimated using wave-cut platforms at ca. 0.7?C0.9?m/ka on the Jalisco block coast, Rivera-North America tectonic plate boundary. We examine reported measurements from marine notches and shoreline angle elevations in conjunction with their radiocarbon ages that indicate surface uplift rates increasing during the Holocene up to ca. 3?±?0.5?m/ka. In contrast, steady rates of uplift (ca. 0.5?C1.0?m/ka) in the Pleistocene and Holocene characterize the Michoacan coastal sector, south of El Gordo graben and north of the Orozco Fracture Zone (OFZ), incorporated within the Cocos-North America plate boundary. Significantly higher rates of surface uplift (ca. 7?m/ka) across the OFZ subduction may reflect the roughness of subducting plate. Absence of preserved marine terraces on the coastal sector across El Gordo graben likely reflects slow uplift or coastal subsidence. Stratigraphic markers and their radiocarbon ages show late Holocene (ca. last 6?ka bp) coastal subsidence on the Guerrero gap sector in agreement with a landscape barren of marine terraces and with archeological evidence of coastal subsidence. Temporal and spatial variability in recent deformation rates on the Mexican Pacific coast may be due to differences in tectonic regimes and to localized processes related to subduction, such as crustal faults, subduction erosion and underplating of subducted materials under the southern Mexico continental margin. 相似文献
103.
Jan-Hendrik May Jana Zech Frank Preusser Jaime Argollo Heinz Veit 《Quaternary Research》2011,76(1):106-118
Although glacial landscapes have previously been used for the reconstruction of late Quaternary glaciations in the Central Andes, only few data exist for the Eastern Cordillera in Bolivia. Here, we present results from detailed morphostratigraphic mapping and new data of surface exposure dating (SED), optically stimulated luminescence (OSL), and radiocarbon dating (14C) from the Huara Loma Valley, Cordillera de Cochabamba (Bolivia). Discrepancies between individual dating methods could be addressed within the context of a solid geomorphic framework. We identified two major glaciations. The older is not well constrained by the available data, whereas the younger glaciation is subdivided into at least four major glacial stages. Regarding the latter, a first advance dated to ~ 29-25 ka occurred roughly contemporaneous with the onset of the global last glacial maximum (LGM) and was followed by a less extensive (re-)advance around 20-18 ka. The local last glacial maximum (LLGM) in the Huara Loma Valley took place during the humid lateglacial ~ 17-16 ka, followed by several smaller readvances until ~ 10-11 ka, and complete deglaciation at the end of the Early Holocene. 相似文献
104.
A diverse fauna of wasps of the extinct parasitoid family Stigmaphronidae (Ceraphronoidea) are recorded in Early Cretaceous (Lower Albian) amber from Spain. Seven new species in five genera are described and figured based on 51 specimens, representing more material than in all the world’s other amber deposits combined. New species include: Elasmophron mari sp. nov., Libanophron sugaar sp. nov., Hippocoon basajauni sp. nov., Burmaphron jentilak sp. nov., B. sorginak sp. nov., B. iratxoak sp. nov., and Tagsmiphron olentzero sp. nov. The significance of the fauna is discussed and compared with that of other Cretaceous amber deposits, in particular the tremendous richness of the Spanish fauna is contrasted with the complete absence of stigmaphronids in the slightly younger and nearby French amber. Whether this stark difference represents particularly favorable conditions for these parasitoids, or their hosts, in the Cretaceous Spanish archipelago, or whether it is owing to taphonomic factors is discussed. 相似文献
105.
Bertha Aguilar Reyes Victoria Mejía Avto Goguitchaichvili Jaime Escobar Germán Bayona Francisco Bautista Juan C. Morales Thomas J. Ihl 《Studia Geophysica et Geodaetica》2013,57(4):741-754
Rock-magnetic investigations of environmental samples, such as soils, dust and leaves, can provide useful information on environmental stress. Aim of this paper is to report on the first magnetic survey carried out on environmental samples from Bogotá, Colombia, which is the fifth most populated city of Latin America. We studied three kinds of samples in order to evaluate their potential as pollution markers: soils, urban dust and leaves of the Sauco (Sambucus nigra) tree. Standard magnetic methods were used to analyze the three groups of samples, with special emphasis on leaves investigated here for the first time for environmental purposes. Samples were collected along two perpendicular transects in an area of the city presumably unpolluted, with two different systems of public transportation. Thermomagnetic curves obtained from soils and atmospheric dust show clearly defined ferrimagnetic phase (probably magnetite) as the main magnetic carrier. Curves of acquisition of isothermal remanent magnetization confirm the ferrimagnetic character of magnetic particles. Frequency-dependent magnetic susceptibility was found between 0 and 10%, suggesting less-important contribution of ultrafine super-paramagnetic magnetite. The apparent contradictory results between soils and the rest of samples may reflect different accumulation period for magnetic particles, being shorter for leaves and urban dust than for soils. 相似文献
106.
Manuel Carbajal-Romero Esteban Flores-Mendez Norberto Flores-Guzmán Jaime Núñez-Farfán Enrique Olivera-Villaseñor Francisco José Sánchez-Sesma 《Geofísica Internacional》2013,52(1):21-30
The present work shows the propagation of Scholte interface waves at the boundary of a fluid in contact with an elastic solid, for a broad range of solid materials. It has been demonstrated that by an analysis of diffracted waves in a fluid it is possible to infer the mechanical properties of the elastic solid medium, specifically, its propagation velocities. For this purpose, the diffracted wave field of pressures and displacements, due to an initial wave of pressure in the fluid, are expressed using boundary integral representations, which satisfy the equation of motion. The source in the fluid is represented by a Hankel’s function of second kind and zero order. The solution to this wave propagation problem is obtained by means of the Indirect Boundary Element Method, which is equivalent to the well-known Somigliana representation theorem. The validation of the results is carried out by using the Discrete Wave Number Method and the Spectral Element Method. Firstly, we show spectra of pressures that illustrate the behavior of the fluid for each solid material considered, then, we apply the Fast Fourier Transform to show results in time domain. Snapshots to exemplify the emergence of Scholte’s waves are also included. 相似文献
107.
R. Chan M. F. A. da Silva Jaime F. Villas?da?Rocha 《Astrophysics and Space Science》2012,337(1):185-191
Using the conventional gravastar model, that is, an object constituted by two components where one of them is a massive infinitely
thin shell and the other one is a de Sitter interior spacetime, we physically interpret a solution characterized by a zero
Schwarzschild mass. No stable gravastar is formed and it collapses without forming an event horizon, originating what we call
a massive non-gravitational object. The most surprise here is that the collapse occurs with an exterior de Sitter vacuum spacetime.
This creates an object which does not interact gravitationally with an outside test particle and it may evolve to a point-like
topological defect. 相似文献
108.
Results of a study of turbiditic deposits in a sequence of middle to late Holocene marine sediments from Alfonso Basin in
the southern Gulf of California are presented. Turbidites are identified from analyses of core sections, X-ray images, texture
and granulometry. Characterization of distal turbidites could be difficult, particularly for thin fine-grained deposits with
little contrast in grain size, mineralogy and texture. We have here included analyses of microfossil and magnetic mineral
data. Turbiditic currents transport material from various depths in the continental slope into the basin and it can be expected
that turbiditic deposits are characterized by re-worked material, lack of microfossils or mixed assemblages with no content
of paleoceanographic and paleoclimatic record. This may show in lack of internal coherence as quantified by factor analysis
of microfossil assemblages. Turbidites in some cases may also show distinct magnetic properties as compared with those in
the sediment sequence. In Alfonso Basin, turbidites show increased contents of detrital magnetic minerals volcanic-derived
and transported from the basin slope. We identify twelve turbiditic layers through the sequence that present high magnetic
susceptibility and low communalities from factor model to the microfossils data providing characterization of the turbidites. 相似文献
109.
110.
Forest cover change in highland pine-oak forests of Michoacan, Mexico is due to a process of conversion of natural forests to avocado orchards. Privately-owned avocado orchards are found on land that was common forest before the 1992 Reform of the Mexican Constitution. We ask how forest cover change was facilitated by policy changes that affected land tenure rules and existing community forestry programs. We use a comparative case study of four communities, an analysis of forest cover change, and interviews and household surveys. Results show that 33.1% of forest cover was lost over a 16-year-period across the region. However, two forestry case study communities lost 7.2% and 15.1% of forest cover, while two adjacent non-forestry communities lost 86.5% and 92.4%, respectively. Interview data show that the Reform of Article 27 combined with the 1992 Forestry Law led to collapse of local governance, illegal division of common forests, and illegal logging in the two non-forestry communities. 相似文献