The Cretaceous (Cenomanian) continental record of the Laje do Coringa flagstone (Alcântara Formation), northeastern South America     

《Journal of South American Earth Sciences》2014

The fossil taxa of the Cenomanian continental flora and fauna of São Luís Basin are observed primarily in the bone bed of the Laje do Coringa, Alcântara Formation. Many of the disarticulated fish and tetrapod skeletal and dental elements are remarkably similar to the chronocorrelate fauna of Northern Africa. In this study, we present a summary of the continental flora and fauna of the Laje do Coringa bone-bed. The record emphasizes the existence of a trans-oceanic typical fauna, at least until the early Cenomanian, which may be interpreted as minor evolutionary changes after a major vicariant event or as a result of a land bridge across the equatorial Atlantic Ocean, thereby allowing interchanges between South America and Africa. The paleoenvironmental conditions in the northern Maranhão State coast during that time were inferred as forested humid areas surrounded by an arid to semi-arid landscape.  相似文献   

Paleoenvironmental setting and description of an estuarine oyster reef in the Eocene of Patagonia,southern Argentina     

《Journal of South American Earth Sciences》2014

A middle Eocene Crassostrea sp. reef near Río Turbio, southwestern Patagonia (Argentina), represents the earliest record of an oyster reef associated with estuarine facies in the southern hemisphere, and also one of the few known worldwide occurring in Paleogene rocks. The reef grew in an outer estuary environment subject to periodic changes in salinity and may have reached a maturing phase. The Río Turbio reef – by its dimensions, geometry, and substrate lithology– would have been located in a tidal channel convergence area. This reef provides new evidence suggesting that estuaries served as refuges for Crassostrea populations allowing them to disperse into fully marine environments many times throughout the Cenozoic.  相似文献   

中国大陆地区GNSS ZTD对超强东部型厄尔尼诺事件的响应     

于腾丽  王勇  黄靖  杨军  占伟 《大地测量与地球动力学》2022,42(10):1015-1019

利用CMONOC提供的GNSS连续观测数据分析天顶对流层延迟（ZTD）代替水汽的可行性,并利用快速傅里叶变换（FFT）和小波变换(WT)开展GNSS ZTD对超强东部型厄尔尼诺事件的响应分析。结果表明,超强东部型厄尔尼诺事件会增加中国大陆地区水汽含量,在热带及亚热带地区响应更为显著;同时该事件会影响GNSS ZTD 的显著变化周期,使9个月的变化周期减弱,0.8~3个月内的变化周期增强。  相似文献   

Putative Meteoritic Craters in Río Cuarto (Central Argentina) Interpreted as Eolian Structures     

Cione  Alberto L.  Tonni  Eduardo P.  San Cristóbal  Jorge  Hernández  Pedro J.  Benítez  Adrián  Bordignon  Fernando  Perí  Jorge A. 《Earth, Moon, and Planets》2002,91(1):9-24

Ten oblong aligned depressions in the Río Cuarto area (provincia de Córdoba, Argentina) were supposed to be the result of very-low-angle Holocene meteoroid impacts. However, we consider that authors that studied the structures did not demonstrated their extraterrestrial origin. We suggest that an eolian origin for the structures of Río Cuarto is more likely. Actually, these landforms integrate large systems of similar deflation/accumulation geoforms aligned according to predominant winds during different periods.  相似文献   

Archean–Ediacaran evolution of the Campos Gerais Domain — A reworked margin of the São Francisco paleocontinent (SE Brazil): Constraints from metamafic–ultramafic rocks     

《地学前缘(英文版)》2022,13(5):101201

The Campos Gerais Domain (CGD) in southeastern Brazil is an approximately 180 km × 35 km area of Archean–Proterozoic rocks located southwest of the São Francisco Craton (SFC). The Archean–Paleoproterozoic evolution of the CGD — alongside its potential correlation with the SFC or other cratonic blocks in the region — is currently poorly-constrained. We present the results of systematic petrography, bulk-rock geochemistry, mineral chemistry and geochronology for a suite of scarcely studied mafic–ultramafic rocks from the CGD. We also provide a compilation of previously reported bulk-rock geochemical and spinel group mineral chemical data for mafic–ultramafic rocks throughout the CGD, and geochronological information for various lithotypes in the region. The CGD records a protracted Mesoarchean to Statherian (3.1–1.7 Ga) crustal evolution, which we interpret to share a common history with the southern SFC and their related reworked segments, suggesting that it is a westward extension of this cratonic terrain. The metavolcano-sedimentary rocks of the Fortaleza de Minas and Alpinópolis segments represent a Mesoarchean greenstone belt that is stratigraphically and chemically comparable to Archean greenstone belts worldwide, and that is broadly coeval with a local suite of tonalite-trondhjemite-granodiorite (TTG) gneisses and migmatites. U-Pb SHRIMP zircon data from a subalkaline metagabbro yielded a concordia age of ca. 2.96 Ga, revealing a previously unrecognized phase of Archean magmatism in the CGD that can be chrono-correlated with metakomatiite and TTG generation elsewhere in the São Francisco paleocontinent. Our data contradict a hypothesis whereby the metavolcano-sedimentary rocks of the Jacuí-Bom Jesus da Penha and Petúnia segments represent an ophiolite, as previously suggested, instead presenting features that point to formation in association with a continental arc. Coupled with a U-Pb (SHRIMP) crystallization age of ca. 2.13 Ga recorded by zircon grains from a metaultramafic rock, these data highlight that a magmatic event was chrono-correlated with the main accretionary phase of the Minas Orogeny, and with the Pouso Alegre/Amparo and São Vicente complexes. Finally, a U-Pb (SHRIMP) concordia age of ca. 590 Ma — obtained from metamorphic-textured zircon grains from a metaultramafic rock — points to a late metamorphic overprint related to upper amphibolite conditions, brittle fault activation and the juxtaposition of crustal blocks in association with the latest stages of western Gondwana’s assembly in the southern SFC, with later retrogression to greenschist-facies.  相似文献   

Old Chico’s new tricks: Neoliberalization and water sector reform in Brazil’s São Francisco River Basin     

《Geoforum》2015

This article examines changing water governance modalities in the context of the neoliberalization of nature. Specifically, it focuses on Brazilian water sector reforms passed in 1997 that mandate decentralized and participatory decision-making at the river basin scale. Critics have suggested that rescaling, decentralization, and participatory governance mechanisms – supposedly intended to render decision-making more equitable, accessible, and relevant – can serve to legitimate, facilitate, and thus further embed processes of neoliberalization. Examining the impact of Brazil’s water sector reforms on the state–society relationship, this article presents a case study of water governance in the São Francisco River Basin and finds that the reforms – despite their neoliberalizing potential – have not significantly contributed to the neoliberalization of governance therein. Instead, water governance continues to be characterized by longstanding patterns of traditional elite control. Through an institutional and socio-natural analysis, this article describes and accounts for the continued dominance of these patterns relative to neoliberalization and explores activists’ efforts to use water sector reforms to pursue more progressive possibilities. The article concludes with a discussion of the implications for variegation and contestation in ongoing debates over neoliberal natures.  相似文献   

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO   总被引：1，自引：1，他引：0  

Marc H. Taylor  Jorge Tam  Vernica Blaskovic  Pepe Espinoza  R. Michael Balln  Claudia Wosnitza-Mendo  Juan Argüelles  Erich Díaz  Sara Purca  Noemi Ochoa  Patricia Ayn  Elisa Goya  Dimitri Gutirrez  Luis Quipuzcoa  Matthias Wolff 《Progress in Oceanography》2008,79(2-4):366

The Northern Humboldt Current Ecosystem is one of the most productive in the world in terms of fish production. Its location near to the equator permits strong upwelling under relatively low winds, thus creating optimal conditions for the development of plankton communities. These communities ultimately support abundant populations of grazing fish such as the Peruvian anchoveta, Engraulis ringens. The ecosystem is also subject to strong inter-annual environmental variability associated with the El Niño Southern Oscillation (ENSO), which has major effects on nutrient structure, primary production, and higher trophic levels. Here our objective is to model the contributions of several external drivers (i.e. reconstructed phytoplankton changes, fish immigration, and fishing rate) and internal control mechanisms (i.e. predator-prey) to ecosystem dynamics over an ENSO cycle. Steady-state models and time-series data from the Instituto del Mar del Perú (IMARPE) from 1995 to 2004 provide the base data for simulations conducted with the program Ecopath with Ecosim. In simulations all three external drivers contribute to ecosystem dynamics. Changes in phytoplankton quantity and composition (i.e. contribution of diatoms and dino- and silicoflagellates), as affected by upwelling intensity, were important in dynamics of the El Niño of 1997–98 and the subsequent 3 years. The expansion and immigration of mesopelagic fish populations during El Niño was important for dynamics in following years. Fishing rate changes were the most important of the three external drivers tested, helping to explain observed dynamics throughout the modeled period, and particularly during the post-El Niño period. Internal control settings show a mix of predator–prey control settings; however a “wasp-waist” control of the ecosystem by small pelagic fish is not supported.  相似文献   

1997–1998 El Niño off Peru: A numerical study     

F. Colas  X. Capet  J.C. McWilliams  A. Shchepetkin 《Progress in Oceanography》2008,79(2-4):138

An eddy-resolving numerical simulation for the Peru–Chile system between 1993 and 2000 is analyzed, mainly for the 1997–1998 El Niño. Atmospheric and lateral oceanic forcings are realistic and contain a wide range of scales from days to interannual. The solution is validated against altimetric observations and the few in situ observations available. The simulated 1997–1998 El Niño closely resembles the real 1997–1998 El Niño in its time sequence of events. The two well-marked, sea-level peaks in May–June and November–December 1997 are reproduced with amplitudes close to those observed. Other sub-periods of the El Niño seem to be captured adequately. Simple dynamical analyses are performed to explain the 1997–1998 evolution of the upwelling in the model. The intensity of the upwelling appears to be determined by an interplay between alongshore, poleward advection (related to coastal trapped waves) and wind intensity, but also by the cross-shore geostrophic flow and distribution of the water masses on a scale of 1000 km or more (involving Rossby waves westward propagation and advection from equatorial currents). In particular, the delay of upwelling recovery until fall 1998 (i.e., well after the second El Niño peak) is partly due to the persistent advection of offshore stratified water toward the coast of Peru. Altimetry data suggest that these interpretations of the numerical solution also apply to the real ocean.  相似文献   

The impact of overfishing and El Niño on the condition factor and reproductive success of Peruvian hake, Merluccius gayi peruanus   总被引：1，自引：1，他引：0  

Michael Balln  Claudia Wosnitza-Mendo  Renato Guevara-Carrasco  Arnaud Bertrand 《Progress in Oceanography》2008,79(2-4):300

In this study we examine physiological responses of Peruvian hake (Merluccius gayi peruanus) to changes in their population structure and physical environment during the period 1971–2004. In particular, we assess the relative investment of energy in growth and/or reproduction of small (20–35 cm) and large (35–50 cm) hake. We calculated the (i) condition (Fulton’s K), (ii) gonad and (iii) gut fullness indices for 42,761 female hakes sampled from commercial landings; these indices indicate fish somatic, reproductive and feeding condition, respectively. Using Generalized Additive Models we then examined potential relationships between these indices and sea surface temperature anomalies and date. Drastic energy exhaustion and a decrease in female hake fecundity were observed during El Niño events. The long-term trend showed a general increase in condition factor and a decrease in gonad index for large hake between 1971 and 2004. Small hake exhibited a different trend with an increase in reproductive activity, which was accompanied by an earlier maturation. We hypothesise that the observed low investment of energy in reproduction by large female hake might be related to the lack of large males, due to a sex-selective fishery and the impact of El Niño. We suggest that fishing diminished hake reproductive capacity, modified the sex ratio in favour of females and increased population vulnerability to environmental stress, in particular to the El Niño. The impact of multidecadal variability and predators like the squid, Dosidicus gigas, remain unresolved until longer time series become available.  相似文献   

A MIXTURE MODEL OF ANNUAL PRECIPITATION IN PERU*     

Thomas D. Tapley  Peter R. Waylen 《The Professional geographer》1989,41(1):62-71

A two component mixed log-normal distribution effectively models annual precipitation totals at two stations in Peru characterized by widely differing interannual patterns of precipitation. Physical evidence supports the division of station records into two subsamples. Years with ENSO events and years without ENSO events identify the components of a mixed probability model. The mixed model produces a superior fit to the two parameter log-normal distribution. Model application provides a reliable means of precipitation prediction and also quantitatively describes the highly variable temporal and spatial pattern of annual precipitation in western Peru.  相似文献