Columbus,the discovery of America,and Russia

The discovery of a new continent that was later called America by Christopher Columbus some five hundred years ago, has in one way or another, influenced people the World over. The extraordinary significance of this event for mankind is displayed by the dimension of the consequences and the variety of reactions among nations and communities of the “Old World”.     

Quaternary records of pika, Ochotona, in North America

Mead, Jim I. 1987 06 01: Quaternary records of pika, Ochotona , in North America. Boreas , Vol. 16, pp. 165–171. Oslo. ISSN 0300–9483.
Pika (Lagomorpha: Ochotona ) have lived in North America since the Hemphillian land mammal age (late Pliocene). At least three species, O. whartoni (extinct giant pika), O. princeps (the living species), and unidentified large and small forms, lived in North America during the Quaternary. Forty-six localities of Quaternary-age pika are recorded. Many localities are actually site clusters, where packrat (Rodentia: Neotoma ) middens or stratified sediments record pika fossils of many ages. Packrat middens in the arid west have provided pika dung pellets directly associated with plant macrofossils. Individual dung pellets provide direct radiocarbon dates and microhistological remains permit dietary reconstructions. Pika lived in northeastern portions of the continent during the Illinoian glacial age and possibly earlier. During the Wisconsinan glacial period, pika stayed in the mountainous west, but an exception exists. It is proposed that pika were not restricted to rocky/talus slopes during the Pleistocene, as is the living species in North America, and therefore should not be used as an indicator of ecological niche. Equable climates (cooler summers) may have been all that was needed for pika to migrate to new territories, areas without talus.     

Zurupleuropholis gen. nov. (Teleostei,Albian, Argentina), first pleuropholids from the Cretaceous of South America

Although the Cretaceous is characterized by a rich fish diversity, Cretaceous continental fishes from Gondwana are poorly known and comparatively scarce. Among these fishes, the family Pleuropholidae is only known by a few species relatively poorly preserved, from the Middle Jurassic to Lower Cretaceous of Europe, Africa, North America, and South America. In this paper, two new species of the pleuropholid new genus Zurupleuropholis are described, Z. quijadensis gen. et sp. nov. and Z. decollavi gen. et sp. nov. The new fishes were recovered in the Lower Cretaceous lacustrine Lagarcito Formation of central-west Argentina. This taxon constitutes a relevant finding considering that the representation of the family Pleuropholidae is rare worldwide. Zurupleuropholis gen. nov. appears to be the youngest known member of Pleuropholidae, and it represents the second record of the family in South America and the first record in the Cretaceous of the continent.     

Paleobotany of Wisconsinan interstadials, eastern Great Lakes region, North America

This study concerns the pollen and plant macrofossils from Mid-Wisconsinan Interstadial sites within the Wisconsinan ice margin in eastern North America. The time period covered is from about 55,000 years BP to 22,500 years BP, an interval much longer than the postglacial. Sediments examined are principally those of large lakes deposited in the Erie and Ontario basins during intervals of ice retreat.The Port Talbot I Interval (from about 55,000 to 50,000 years BP) in the Erie basin is characterized by pollen assemblages alternating from Pinus-dominated zones to ones with abundant Pinus, Quercus, and nonarboreal pollen. These assemblages are interpreted as indicating relatively warm and dry conditions. Mean July temperatures fluctuated between 15 and 21°C.During the succeeding Port Talbot II Interval and Plum Point Interstadial, in both the Erie and Ontario basins, pollen assemblages are characterized by dominant Pinus and Picea. Characteristic macrofossils include needles of the boreal Picea and Larix and leaves of species with a more northerly distribution, such as Dryas integrifolia, Betula glandulosa var. glandulosa, Vaccinium uliginosum var. alpinum, and Salix herbacea. These fossil assemblages are interpreted as indicating cooler and moister conditions in a forest-tundra environment. Mean July temperatures fluctuated between 10 and 15°C during the Port Talbot II Interval and Plum Point Interstadial.     

The ecology of hazardousness,the experience of South America

In many parts of South America, the socio-economic condition of the population is such that in many respects the people, because of their vulnerable state, are a disaster waiting to occur. The triggering action of the disaster will be an extreme physical or biophysical event. If any advance is to be made in natural hazard management, then the focus must be upon people first. Halt the process of underdevelopment in South American societies and you have taken a major step forward in natural hazard management. The major concern of this paper is not so much with the competition for first place in hazard proneness in South America, but rather the elaboration of the total ecology of what we commonly designate as disasters, which ordinarily occur at the interface of extreme natural phenomena and vulnerable settlement patterns, and which should be seen, as the extreme situation which is implicit in the everyday condition of the population. Vulnerability is the key concept in this relationship. South American nations vary greatly in their hazard proneness, in the vulnerability of sectors in their societies, in the losses and general repercussions of hazardous events, and in their ability to cope effectively with the post-disaster situation, either alone or with international aid.     

Geochemical characterization of surface waters and groundwater resources in the Managua area (Nicaragua,Central America)

This paper reports new geochemical data on dissolved major and minor constituents in surface waters and ground waters collected in the Managua region (Nicaragua), and provides a preliminary characterization of the hydrogeochemical processes governing the natural water evolution in this area. The peculiar geological features of the study site, an active tectonic region (Nicaragua Depression) characterized by active volcanism and thermalism, combined with significant anthropogenic pressure, contribute to a complex evolution of water chemistry, which results from the simultaneous action of several geochemical processes such as evaporation, rock leaching, mixing with saline brines of natural or anthropogenic origin. The effect of active thermalism on both surface waters (e.g., saline volcanic lakes) and groundwaters, as a result of mixing with variable proportions of hyper-saline geothermal Na–Cl brines (e.g., Momotombo geothermal plant), accounts for the high salinities and high concentrations of many environmentally-relevant trace elements (As, B, Fe and Mn) in the waters. At the same time the active extensional tectonics of the Managua area favour the interaction with acidic, reduced thermal fluids, followed by extensive leaching of the host rock and the groundwater release of toxic metals (e.g., Ni, Cu). The significant pollution in the area, deriving principally from urban and industrial waste-water, probably also contributes to the aquatic cycling of many trace elements, which attain concentrations above the WHO recommended limits for the elements Ni (∼40 μg/l) and Cu (∼10 μg/l) limiting the potential utilisation of Lake Xolotlan for nearby Managua.     

Evolution of late Triassic rift basin evaporites (Passaic Formation): Newark Basin, Eastern North America

The Passaic Formation of the late Triassic Newark Supergroup is 2700 m thick and was deposited in series of wide, deep to shallow lacustrine environments in the Newark rift basin (eastern North America). The Passaic Formation can be divided into lower, middle, and upper sections based on depositional structures, composition and the distribution and morphology of its evaporites. Evaporites formed as a result of syndiagenetic cementation and/or displacive processes. Evaporitive minerals now include gypsum and anhydrite, although other mineral species, such as glauberite, may have originally existed. Most of the evaporites of the Passaic Formation occur within massive red mudstone and siltstone lithologies in the form of diffuse cements, void-fillings, euhedral crystals, crystal clusters and nodules. These evaporites grew displacively within the fine siliciclastic matrix as a result of changes in the hydrochemical regimes of the rift basin. A well-developed upward increase in the amount of evaporite material is present in the Passaic Formation. This resulted from: (1) long-term, progressive increase in aridity, and (2) significant increase in evaporation surface area of the basin during its tectonic evolution. A nonmarine source for the evaporites is evident from the isotopic data. Sulphate δ³⁴S ranges from 11%. to 3.3%. CDT, while δ¹⁸O ranges from + 15.1%. to + 20.9%. SMOW, indicating derivation from early diagenetic oxidation of organic sulphur and pyrite within the organic-rich, lacustrine deposits. The ⁸⁷Sr/⁸⁶Sr ratios in sulphate are radiogenic (average 0.71211), showing the interaction of basin waters with detrital components and that the Newark Basin was isolated from the world ocean. Most of the original evaporites show evidence of diagenetic change to polycrystalline and polymineralic pseudomorphs now filled with recrystallized coarse-grained anhydrite (1–3 mm size) and low-temperature albite. Homogenization temperatures of fluid inclusions within the coarse-grained anhydrite indicate crystallization temperatures for anhydrite in the range of 150° to 280°C. Such elevated temperatures resulted from circulation of hot water in the basin. Later exhumation of these rocks caused partial to total replacement of anhydrite by gypsum in the upper part of the section. The resulting increase in volume due to hydration of anhydrite at shallow depths also emplaced non-evaporative satin-spar veins (fibrous gypsum) along bedding planes and in fractures. While the local geology of the Newark rift basin controlled the distribution of facies, the sedimentological development of the Passaic Formation evaporites resulted from the world-wide climatic aridity that prevailed during the late Triassic. because the Newark Basin sequence was only covered with about 3 km of sedimentary overburden that correspond to about 100°C and hence suggests that evaporites have experienced alteration by hot fluids. 5 As the Triassic marks the greatest evaporite formation world-wide and profound sense of parched continentality throughout the world existed before the final break-up of the Pangea, the Passaic Formation evaporites are an example of the influence of these palaeoclimatic conditions at the eastern margin of North America.     

Diagenesis of the Newark Rift Basin, Eastern North America

Late Triassic nonmarine strata in the Newark Rift Basin, eastern North America, accumulated in a subsiding half-graben prior to opening of the Atlantic Ocean. These strata consist, in ascending order, of the Stockton, Lockatong, and Passaic formations. Although different in specific lithology, these formations all exhibit diagenetic fabrics dominated by authigenic albite and analcime. These same minerals have a similar presence in Late Triassic (Newark Supergroup) strata of other rift-related basins to the north, suggesting that related authigenesis is not simply a result of local diagenetic factors. The basal deposit, the Stockton Formation, is composed of fluvial sandstones and overbank mudstones, with nodular pedogenic calcite (calcrete). During burial, original micrite was first recrystallized into sparry calcite and then later subjected to partial replacement by authigenic albite, which is also present as overgrowths and void fillings in overbank mudstones. The Lockatong Formation contains organic-rich shales, carbonates, and evaporative mudstones deposited under cyclic conditions in laterally extensive lacustrine environments. Analcime comprises up to 40% of these strata by volume, occurring within the matrix, as a replacement of original carbonates and evaporites, and as fillings in macrovoids. The overlying Passaic Formation is made up of massive red mudstones, evaporites, and local calcareous lacustrine sequences. Evaporites are replaced by coarse-grained anhydrite together with some authigenic albite. A central question concerns the source for the Na, Si, and Al required for albite and analcime authigenesis. It is suggested that, in addition to alteration of primary siliciclastic material, sodium in particular was supplied in two ways: (1) from high concentrations in original evaporative brines and groundwaters (Lockatong and Passaic formations); and (2) from dissolution of associated sodium-bearing evaporites (Lockatong and Passaic Formation) during diagenesis. It is proposed here that basin-sourced, Na-enriched brines circulated through the section over time. As albite is more stable at elevated temperatures relative to analcime, it developed in the lowermost strata of the basin (Stockton Formation). Analcime is more prevalent in the overlying Lockatong Formation.     

Red pandas (Mammalia,Carnivora: Parailurus) in the biomes of North Eurasia and North America

The discovery of the Pliocene red panda (Parailurus) in the West Transbaikal area, as well as Asian raccoons in North Eurasia and North America, indicates that forested areas with bamboo bushes were wide-spread in the Holarctic during the Neogene. During the Late Pliocene, due to a gradual cooling of the climate, altiplanation, and other factors, their habitat started disintegrating, and red pandas began dying out, surviving only in China.     

Anorthosite massifs,rapakivi granites,and late proterozoic rifting of north America

Anorthosite—adamellite complexes are the chief manifestations of Elsonian magmatic activity of Paleohelikian age (about ?1500 to ?1400 Ma) in Labrador, Canada. Magmatism of similar age and anorogenic character, though with fewer occurrences of massif anorthosite, is present in a belt across the mid-continent and southwestern United States. Anorthosite—quartz mangerite complexes in the Grenville Province lie along the trend of this belt and, although few ages older than the profound Grenvillian regional metamorphism about ?1100 Ma have been determined on them, circumstantial evidence suggests that these also are dominantly of Paleohelikian age.The Labrador complexes are intruded into high-grade metamorphic terrane, older by at least 200 to 300 Ma than the Elsonian magmatism. Typical association of anorthosite massifs with high-grade metamorphic terranes, in Labrador and elsewhere, is probably due to their intrusion into older, stabilized, cratonic crust. The anorthosite—adamellite (and anorthosite—quartz mangerite) complexes are products of bimodal magmatism, and an anorogenic cratonic setting is considered to be of fundamental importance to development of the suites. Olivine tholeiite magmas fractionate to produce high-A1 tholeiitic magmas at or near the base of the cratonic crust, and these magmas are the parents from which anorthosite massifs develop by plagioclase fractionation at higher levels within the crust. Adamellite (quartz mangerite) magmas develop mainly by partial fusion of deep crustal rocks, caused by heat of crystallization from the fractionating olivine tholeiite magmas in the staging region, at or near the base of the crust, and are intruded upward into the crustal complexes; rapakivi textures and chemistries are characteristic products of these magmas. Ferrodiorites, widely associated with anorthosite massifs, probably form as late-stage fractionation products of basic magmas in the subcrustal staging region and are intruded into the massifs in their final stages of development (before intrusion of adamellite or quartz mangerite magmas).The Neohelikian record, dominated by terrestrial sedimentation, basaltic extrusive and intrusive activity, and alkalic magmatism, began soon after ?1400 Ma in the mid-continent United States, central Labrador and southern Greenland. The lithological assemblages have been interpreted by several authors as similar to those of intracontinental rift zones. The following sequence of events: intrusion of Paleohelikian anorthosite—adamellite complexes (granitic intrusion and/or rhyolitic extrusion only, in some places), strong uplift and erosion, crustal attenuation causing basin formation, Neohelikian terrestrial sedimentation, rifting or incipient rifting, renewed basaltic magmatism, and alkalic magmatism, is believed to record a continuing evolving process of mantle—crust interactions over a broad belt across North America.     

A new species of the genus Echinorhinus (Chondrichthyes,Echinorhiniformes) from the upper cretaceous of southern South America (Argentina-Chile)

We describe isolated shark teeth collected from levels of the Calafate Formation at the SE coast of the Argentino Lake, Calafate city, Santa Cruz province, Argentina (Atlantic Ocean), and from the Algarrobo coast at the Valparaíso Region in central Chile (Pacific Ocean). The teeth belong to a new species of the echinorhiniform genus Echinorhinus. Echinorhinus maremagnum n. sp. was a taxon distributed in both the southwestern Atlantic and the southeastern Pacific. This new taxon constitutes the oldest record of echinorhiniforms from South America and one of the few Mesozoic records at a worldwide scale.     

拉丁美洲大地构造轮廓、成矿区带和成矿系列

拉丁美洲是全世界矿产资源最丰富的地区之一。总结该地区的成矿地质背景、划分成矿区带、研究成矿系列将对进一步规划勘查和开发起到指导作用。在大地构造轮廓方面分成3个构造亚域,对次级构造单元的划分方案进行了探讨。在成矿区带划分方面,按5级成矿区带的划分方案,对一级成矿域和二级成矿省进行了划分,三级及其以下的成矿单元,对前人的划分方案作了扼要的比较。在成矿系列方面以大地构造演化为主导,以成矿作用和矿床类型为标志,将有内在成因联系的一系列矿床整合成一个成矿系列,并细分为成矿亚系列和成矿组合。     

Diet and habitat of toxodont megaherbivores (Mammalia, Notoungulata) from the late Quaternary of South and Central America

The toxodont megaherbivores Toxodon and Mixotoxodon were endemic to South and Central America during the late Quaternary. Isotopic signatures of 47 toxodont teeth were analyzed to reconstruct diet and ancient habitat. Tooth enamel carbon isotope data from six regions of South and Central America indicate significant differences in toxodont diet and local vegetation during the late Quaternary. Toxodonts ranged ecologically from C₃ forest browsers in the Amazon (mean δ¹³C = −13.4‰), to mixed C₃ grazers and/or browsers living either in C₃ grasslands, or mixed C₃ forested and grassland habitats in Honduras (mean δ¹³C = −9.3‰), Buenos Aires province, Argentina (δ¹³C = −8.7‰), and Bahia, Brazil (mean δ¹³C = −8.6‰), to predominantly C₄ grazers in northern Argentina (δ¹³C = −4.4‰), to specialized C₄ grazers in the Chaco of Bolivia (δ¹³C = −0.1‰). Although these toxodonts had very high-crowned teeth classically interpreted for grazing, the isotopic data indicate that these megaherbivores had the evolutionary capacity to feed on a variety of dominant local vegetation. In the ancient Amazon region, carbon isotope data for the toxodonts indicate a C₃-based tropical rainforest habitat with no evidence for grasslands as would be predicted from the Neotropical forest refugia hypothesis.     

Late Pliocene Glyptodontinae (Xenarthra,Cingulata, Glyptodontidae) of South and North America: Morphology and paleobiogeographical implications in the GABI

Knowledge of the main aspects of the Great American Biotic Interchange (GABI) concerning the glyptodontine Glyptodontidae (Xenarthra) is very scarce. A bidirectional dispersal process was recently proposed for this clade, with the presence of the North American genus Glyptotherium Osborn recognized in latest Pleistocene sediments of northern South America (Venezuela and Brazil). However, the earliest stages of this paleobiogeographical process remain poorly understood, mainly because of the limited fossil record on this clade in late Pliocene sediments. The goals of this contribution are: a) to present and describe the first record of a glyptodontine glyptodontid from the late Pliocene of northern South America, tentatively assigned to a new species of Boreostemma Carlini et al. (Boreostemma? sp. nov); and b) to analyze its paleobiogeographical implications with respect to the GABI. This new material was recovered from the San Gregorio Formation (late Pliocene, prior the GABI) in northern Venezuela, where it is represented by several osteoderms of the dorsal carapace. A comparison among the three known late Pliocene glyptodontine glyptodontids of a) southern South America (Paraglyptodon), b) northern South America (Boreostemma), and c) southern North America ("Glyptotherium"), reveals a series of shared characters between (b) and (c), not present in (a). The most important of these shared characters in (b) and (c) are: all the osteoderms present a great development of the central figure, which is always larger than the peripherals; the sulcus that delimits the central and peripheral figures is narrower and shallower; and all the osteoderms present are relatively thin. This evidence suggests that the lineage of Glyptodontinae which participated in the GABI and subsequently diversified in North America originated in northern South America. Moreover, the evident morphological differences between these glyptodontines with respect to the southern South American forms show a significant separation of both lineages since at least latest Miocene-early Pliocene.     

Seismic hazard maps of Mexico, the Caribbean, and Central and South America

The growth of megacities in seismically active regions around the world often includes the construction of seismically unsafe buildings and infrastructures due to an insufficient knowledge of existing seismic hazard and/or economic constraints. Minimization of the loss of life, property damage, and social and economic disruption due to earthquakes depends on reliable estimates of seismic hazard. We have produced a suite of seismic hazard estimates for Mexico, the Caribbean, and Central and South America. One of the preliminary maps in this suite served as the basis for the Caribbean and Central and South America portion of the Global Seismic Hazard Map (GSHM) published in 1999, which depicted peak ground acceleration (pga) with a 10% chance of exceedance in 50 years for rock sites. Herein we present maps depicting pga and 0.2 and 1.0 s spectral accelerations (SA) with 50%, 10%, and 2% chances of exceedance in 50 years for rock sites. The seismicity catalog used in the generation of these maps adds 3 more years of data to those used to calculate the GSH Map. Different attenuation functions (consistent with those used to calculate the U.S. and Canadian maps) were used as well. These nine maps are designed to assist in global risk mitigation by providing a general seismic hazard framework and serving as a resource for any national or regional agency to help focus further detailed studies required for regional/local needs. The largest seismic hazard values in Mexico, the Caribbean, and Central and South America generally occur in areas that have been, or are likely to be, the sites of the largest plate boundary earthquakes. High hazard values occur in areas where shallow-to-intermediate seismicity occurs frequently.