Spatial and temporal variations of sound in an Andean City: Cajamarca,Peru

This study provides a preliminary examination of the temporal and geographic variations of sound in Cajamarca, a provincial city in the Andes of northern Peru. Sound levels were sampled in four neighborhoods of the city each representing different land-use characteristics and hypothetically distinct environmental sound profiles. The sample sites included the central plaza, the business district, a residential neighborhood, and a small residential community on the urban periphery. Sound readings were taken each hour between 6 am and 12 pm on every day of the week. Sound profiles for each location for a weekday, a Saturday, and a Sunday are presented. Distinct decibel profiles emerge, both geographically and temporally. These changing sound patterns reflect the activities of the town's residents as they move between home, work, and social/recreational activities during the course of a week. Cajamarca's sound profiles are believed to be characteristic of other provincial cities throughout the Andean region.     

Aluminium in Lake Cuicocha,Ecuador, an Andean Crater Lake: Filterable,Gelatinous and Microcrystal Al Occurrence

In Lake Cuicocha watershed, a young caldera lake, soils consist of volcanic deposits with a high SiO₂ and Al₂O₃ content; these andisols are in an early stage of development; and in drainage water from the watershed, aluminium concentrations reach 15.0 μmol L⁻¹. Total aluminium concentrations in Lake Cuicocha water raises up to 7.2 μmol L⁻¹, with nearly 70% occurring as filterable Al at neutral to weak alkaline conditions. Al polymerization to gelatinous aggregates of a few hundred micrometres in diameter as well as the occurrence of Al microcrystals like gibbsite as an ageing product of gelatinous Al polymers was noted in the lake water. The gelatinous Al leads to the formation of larger aggregates resulting in flocs of bacteria, algae, microorganisms and detritus.     

甘肃宝积山盆地中侏罗世植物群特征及古生态、古气候研究

本文对甘肃宝积山盆地窑街组植物大化石进行了系统研究,经鉴定共有19属50种,结合已有的宝积山盆地中侏罗世植物化石资料,发现甘肃宝积山盆地中侏罗世植物群由27属73种组成。其中,银杏类植物10属30种,真蕨类植物5属26种,松柏类植物5属6种,楔叶类植物3属5种,苏铁类植物2属4种,裸子植物球果和种子化石2属2种。基于当前植物群组成特征,对植物化石埋藏学特性进行分析,确定植物化石主要为原地埋藏或亚原地埋藏,少数属种为异地埋藏,并通过对化石类群古生态特征进行分析,结合现生植物的生存环境,初步重建了宝积山盆地中侏罗世植物群落,划分为四个植物群落:岸边—湿地楔叶类植物群落、低地蕨类—苏铁类植物群落、坡地银杏类植物群落和高地松柏类植物群落。通过对植物群组成特征和植物化石叶相特征的统计分析,并与其他气候带植物群特征进行对比,推断中侏罗世时期甘肃宝积山盆地为温暖潮湿的暖温带气候。     

Subducted seamounts in an eclogite-facies ophiolite sequence: the Andean Raspas Complex, SW Ecuador

The metamorphic Raspas Complex of southwest Ecuador consists of high-pressure mafic, ultramafic, and sedimentary rocks. The Lu–Hf ages of a blueschist, a metapelite, and an eclogite overlap at around 130 Ma and date high-pressure garnet growth. Peak metamorphic conditions in the eclogites reached 1.8 GPa at 600°C, corresponding to a maximum burial depth of ~60 km. The geochemical signatures of the eclogites suggest that their protoliths were typical mid-ocean ridge basalts (MORB), whereas the blueschists exhibit seamount-like characteristics, and the eclogite-facies peridotites seem to represent depleted, MORB-source mantle. That these rocks were subjected to similar peak PT conditions contemporaneously suggests that they were subducted together as an essentially complete section within the slab. We suggest that this section became dismembered from the slab during burial at great depth—perhaps as a consequence of scraping off the seamounts. The spatially close association of MORB-type eclogite, seamount-type blueschist, serpentinized peridotite, and metasediments points to an exhumed high-pressure ophiolite sequence.     

Ceramic production during the Middle Horizon: Wari and Tiwanaku clay procurement in the Moquegua Valley,Peru

As the only place simultaneously occupied by the Middle Horizon (A.D. 600–1000) Andean states, the Tiwanaku and the Wari, the Moquegua Valley in southern Peru is of critical importance to understanding relations between the two states. Visual studies of Tiwanaku and Wari ceramics in the valley have elucidated differences in form and decoration. The procurement of raw clays was central to the production of these ceramics, and understanding where people procured their clay may provide insight into the social and economic interactions between these two states. Survey of the Moquegua Valley indicates the extensive availability of raw clays. Results of laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) analyses of clays indicate that there is heterogeneity in the chemical signature of the valley's clays and that at least five different clay groups can be distinguished. Comparison of these clays with LA‐ICP‐MS analysis of ceramics from a Tiwanaku site and a Wari site demonstrates that although Tiwanaku and Wari colonists in Moquegua used locally available clays during the Middle Horizon, the clay sources exploited by potters from each state were different and derived from areas located within their respective middle and upper valley territories. This information provides a basis for future chemical analysis of ceramics from the Moquegua Valley and improved understanding of past social and economic interactions. © 2009 Wiley Periodicals, Inc.     

Paleoentomology and paleoecology of a possible sangamonian site near Innerkip,Ontario

A stream section near Innerkip, Ontario, exposes several meters of organic silts and peaty detritus beneath two late Wisconsinan tills. Radiocarbon dates provide a minimal middle Wisconsinan age of >50,000 yr B.P. A 250-kg bulk sample from the peat stratum was processed for vertebrates, plant macrofossils, and insects. Vertebrate remains include teeth from deer, muskrat, and vole as well as plates from a turtle shell. At least 6000 insect fragments from a minimum of 19 Coleoptera families were identified. The most common groups are hydrophilids and dytiscids (water beetles), curculionids (weevils), staphylinids (rove beetles), and carabids (ground beetles). The majority of identified beetles are associated with fresh water as aquatic predators, scavengers, or grazers, while others prefer hygric substrates and moist plant litter. The large number of plant-dependent beetles, the numerous floating and emergent aquatic plant seeds, and the presence of the associated vertebrates point toward a locally rich and varied flora and fauna, probably deposited in a well-vegetated pond. The modern distributions and ecologies of the identified fossil insects suggest temperatures similar to those found in southern Ontario today. On these grounds the Innerkip peat represents either a very warm interstadial or a possible interglacial deposit. If the latter is true this is the second presumed Sangamon-aged site known in southern Ontario.     

Climate change and tropical Andean glaciers: Past,present and future

Observations on glacier extent from Ecuador, Peru and Bolivia give a detailed and unequivocal account of rapid shrinkage of tropical Andean glaciers since the Little Ice Age (LIA). This retreat however, was not continuous but interrupted by several periods of stagnant or even advancing glaciers, most recently around the end of the 20th century. New data from mass balance networks established on over a dozen glaciers allows comparison of the glacier behavior in the inner and outer tropics. It appears that glacier variations are quite coherent throughout the region, despite different sensitivities to climatic forcing such as temperature, precipitation, humidity, etc. In parallel with the glacier retreat, climate in the tropical Andes has changed significantly over the past 50–60 years. Temperature in the Andes has increased by approximately 0.1 °C/decade, with only two of the last 20 years being below the 1961–90 average. Precipitation has slightly increased in the second half of the 20th century in the inner tropics and decreased in the outer tropics. The general pattern of moistening in the inner tropics and drying in the subtropical Andes is dynamically consistent with observed changes in the large-scale circulation, suggesting a strengthening of the tropical atmospheric circulation. Model projections of future climate change in the tropical Andes indicate a continued warming of the tropical troposphere throughout the 21st century, with a temperature increase that is enhanced at higher elevations. By the end of the 21st century, following the SRES A2 emission scenario, the tropical Andes may experience a massive warming on the order of 4.5–5 °C. Predicted changes in precipitation include an increase in precipitation during the wet season and a decrease during the dry season, which would effectively enhance the seasonal hydrological cycle in the tropical Andes.These observed and predicted changes in climate affect the tropical glacier energy balance through its sensitivity to changes in atmospheric humidity (which governs sublimation), precipitation (whose variability induces a positive feedback on albedo) and cloudiness (which controls the incoming long-wave radiation). In the inner tropics air temperature also significantly influences the energy balance, albeit not through the sensible heat flux, but indirectly through fluctuations in the rain–snow line and hence changes in albedo and net radiation receipts.Given the projected changes in climate, based on different IPCC scenarios for 2050 and 2080, simulations with a tropical glacier–climate model indicate that glaciers will continue to retreat. Many smaller, low-lying glaciers are already completely out of equilibrium with current climate and will disappear within a few decades. But even in catchments where glaciers do not completely disappear, the change in streamflow seasonality, due to the reduction of the glacial buffer during the dry season, will significantly affect the water availability downstream. In the short-term, as glaciers retreat and lose mass, they add to a temporary increase in runoff to which downstream users will quickly adapt, thereby raising serious sustainability concerns.     

Lithospheric evolution of the Andean fold–thrust belt, Bolivia, and the origin of the central Andean plateau

We combine geological and geophysical data to develop a generalized model for the lithospheric evolution of the central Andean plateau between 18° and 20° S from Late Cretaceous to present. By integrating geophysical results of upper mantle structure, crustal thickness, and composition with recently published structural, stratigraphic, and thermochronologic data, we emphasize the importance of both the crust and upper mantle in the evolution of the central Andean plateau. Four key steps in the evolution of the Andean plateau are as follows. 1) Initiation of mountain building by 70 Ma suggested by the associated foreland basin depositional history. 2) Eastward jump of a narrow, early fold–thrust belt at 40 Ma through the eastward propagation of a 200–400-km-long basement thrust sheet. 3) Continued shortening within the Eastern Cordillera from 40 to 15 Ma, which thickened the crust and mantle and established the eastern boundary of the modern central Andean plateau. Removal of excess mantle through lithospheric delamination at the Eastern Cordillera–Altiplano boundary during the early Miocene appears necessary to accommodate underthrusting of the Brazilian shield. Replacement of mantle lithosphere by hot asthenosphere may have provided the heat source for a pulse of mafic volcanism in the Eastern Cordillera and Altiplano at 24–23 Ma, and further volcanism recorded by 12–7 Ma crustal ignimbrites. 4) After 20 Ma, deformation waned in the Eastern Cordillera and Interandean zone and began to be transferred into the Subandean zone. Long-term rates of shortening in the fold–thrust belt indicate that the average shortening rate has remained fairly constant (8–10 mm/year) through time with possible slowing (5–7 mm/year) in the last 15–20 myr. We suggest that Cenozoic deformation within the mantle lithosphere has been focused at the Eastern Cordillera–Altiplano boundary where the mantle most likely continues to be removed through piecemeal delamination.     

中国晚新生代食肉目演替及其古生态意义

本研究系统回顾了中国晚新生代食肉目的演化以及食肉目动物群的演替关系。以属、族或亚科为单位,探讨了我国新近纪和第四纪时期食肉目13个科成员的地史分布和相关类群的生态习性。根据食肉目亚科一级别的演替规律,探讨了中国晚新生代的气候环境变化,支持以下观点：在早中新世气候相对温和,食肉目组成上包含较多的古老、不擅长奔跑的类型;中中新世开始气候趋于干旱化,出现一些四肢修长、擅长在开阔地区追击猎物的类型;晚中新世时期华北气候强烈干旱化,出现了大量以鬣狗科为代表的适应开阔环境的属种,但一些林地组分依然存在,指示这个时期的环境并非典型的草原,依然有较多树木存在;上新世时期华北气候再次变得温暖湿润,鬣狗科大量灭绝,灵猫科等东洋界分子北上;第四纪时期随着冰期的到来,华北再次变成以开阔环境主导,而华南地区一直较为稳定,为温暖湿润的森林环境主导。

     

Quaternary alluvial terraces in an active tectonic region: the San Juan River Valley,Andean Ranges,San Juan Province,Argentina

The San Juan River, located in San Juan Province (Argentina), crosses the Precordillera and other geologic units including the Ullum tectonic valley and the La Laja Zone between latitudes 31°S and 32°S. The San Juan River is antecedent as is suggested by its two perpendicular segments linked by an almost parallel segment to the main structural trend. Along the Precordillera, the San Juan River valley has many different alluvial fans at the river junctions with its tributaries. The Quaternary alluvial fans display surfaces cut in a series of steps which we consider to be alluvial terraces generated by aggradation and repeated incision episodes. The studied sector includes one area with recent major seismic activity (La Laja Zone), another without major seismic activity (Precordillera area), and a subsident area (Ullum area) where a large lake was formed 6500 yr BP. The old San Juan River was captured by the Quebrada de Ullum valley by means of a 25-m incision, which resulted in river-gradient headward erosion. The San Juan River gradient shows some irregularities that, although unrelated to the main structures, are associated with river dynamics, which emphasizes lithologic differences. The main river valley width, the geometry and gradient of each tributary, together with the basement rock lithologies and the size of each local source area are the major factors which control the alluvial terrace generation processes. In the La Laja Zone, where the uppermost terrace is capped by travertine, dating of travertine deposits suggests that the maximum incision rate is 0.9–1 mm/yr related to episodic activity on the La Laja Fault.     

The westward lithospheric drift,its role on the subduction and transform zones surrounding Americas:Andean to cordilleran orogenic types cyclicity

We investigate the effect of the westerly rotation of the lithosphere on the active margins that surround the Americas and find good correlations between the inferred easterly-directed mantle counterflow and the main structural grain and kinematics of the Andes and Sandwich arc slabs.In the Andes,the subduction zone is shallow and with low dip,because the mantle flow sustains the slab;the subduction hinge converges relative to the upper plate and generates an uplifting doubly verging orogen.The Sandwich Arc is generated by a westerly-directed SAM(South American) plate subduction where the eastward mantle flow is steepening and retreating the subduction zone.In this context,the slab hinge is retreating relative to the upper plate,generating the backarc basin and a low bathymetry single-verging accretionary prism.In Central America,the Caribbean plate presents a more complex scenario:(a) To the East,the Antilles Arc is generated by westerly directed subduction of the SAM plate,where the eastward mantle flow is steepening and retreating the subduction zone.(b) To the West,the Middle America Trench and Arc are generated by the easterly-directed subduction of the Cocos plate,where the shallow subduction caused by eastward mantle flow in its northern segment gradually steepens to the southern segment as it is infered by the preexisting westerly-directed subduction of the Caribbean Plateau.In the frame of the westerly lithospheric flow,the subduction of a divergent active ridge plays the role of introducing a change in the oceanic/continental plate's convergence angle,such as in NAM(North American)plate with the collision with the Pacific/Farallon active ridge in the Neogene(Cordilleran orogenic type scenario).The easterly mantle drift sustains strong plate coupling along NAM,showing at Juan de Fuca easterly subducting microplate that the subduction hinge advances relative to the upper plate.This lower/upper plate convergence coupling also applies along strike to the neighbor continental strike slip fault systems where subduction was terminated(San Andreas and Queen Charlotte).The lower/upper plate convergence coupling enables the capture of the continental plate ribbons of Baja California and Yakutat terrane by the Pacific oceanic plate,transporting them along the strike slip fault systems as para-autochthonous terranes.This Cordilleran orogenic type scenario,is also recorded in SAM following the collision with the Aluk/Farallon active ridge in the Paleogene,segmenting SAM margin into the eastwardly subducting Tupac Amaru microplate intercalated between the proto-LiquineOfqui and Atacama strike slip fault systems,where subduction was terminated and para-autochthonous terranes transported.In the Neogene,the convergence of Nazca plate with respect to SAM reinstalls subduction and the present Andean orogenic type scenario.     

Taxonomic composition,paleoecology and biostratigraphy of Late Cretaceous diatoms from Devon Island,Nunavut, Canadian High Arctic

Upper Cretaceous sediments of the Kanguk Formation exposed in Eidsbotn and Viks Fiord grabens on Devon Island, Nunavut, Canadian High Arctic, yielded 91 fossil marine diatom species and varieties (including indeterminate taxa), representing 41 genera. Excellent preservation of the assemblages was aided by shallow burial, protection in downfaulted linear grabens, and the presence of abundant volcanic material. Planktonic species and resting spores comprise nearly 70% of the diatom assemblage, and provided abundant food resources for the Late Cretaceous Arctic ecosystem. Deposition of the approximately 225 m-thick stratigraphic sequence was predominantly in a shallow marine neritic setting, with an upward progression to interbedded terrestrial deposits of the Expedition Fiord Formation, reflecting a regression and eventual persistence of terrestrial facies into the Early Cenozoic. The Kanguk Formation is widespread across the Canadian Arctic, and diatom biostratigraphy indicates a Santonian–Campanian age for the sequences reported herein, based on the presence of Gladius antiquus in the lowermost strata and occurrence of Costopyxis antiqua throughout the succession. However, Amblypyrgus sp. A and Archepyrgus sp. aff. A. melosiroides, encountered in the lower part of the succession, are known exclusively from the Lower Cretaceous. This may suggest a slightly older age. New information on shallow shelf diatom assemblages from this study is compared to reports on two other Late Cretacous Arctic diatom assemblages. These three sites represent an environmental transect from shallow to distal shelf settings and into the oceanic realm.     

Geology and paleoecology of a mid-Wisconsin peat from the Queen Charlotte Islands, British Columbia, Canada

A peat bed on east-central Graham Island of the Queen Charlotte Islands occurs within a nonglacial fluvial succession that is both overlain and underlain by glacial deposits. Radiocarbon dates of 27,500 ± 400 and 45,700 ± 970 yr B.P. at the top and base of the peat, respectively, indicate that it was deposited during the mid-Wisconsin nonglacial interval. The peat is the first documented mid-Wisconsin organic deposit in northern coastal areas of British Columbia. Three local pollen zones are represented. The lowest zone (PM-1) is restricted to sandy silt directly underlying the dated peat. Very high Cyperaceae and moderate Poaceae pollen percentages characterize zone PM-1, and a variety of other herbs are common, suggesting an open landscape rather than a forested one. The middle zone (PM-2) is characterized by abundant pollen of Picea, Tsuga mertensiana, and Cyperaceae, and also contains pollen of Abies, a genus now absent from the Queen Charlotte Islands. Graham Island probably had extensive forests at this time, but abundant pollen and macrofossils of Cyperaceae and emergent aquatics such as Hippuris vulgaris, Veronica scutellata, Potentilla palustris, and Menyanthes trifoliata indicate that there also were open wetland areas. Zone PM-3 also contains abundant arboreal pollen. Large amounts of Sphagnum spores and Selaginella selaginoides megaspores indicate succession of the wetland area at the sample site to a peat bog. Paleoecological analysis of the data suggests that subalpine vegetation elements were depressed by at least 400 m, probably due to a cooler climate. Probable modern analogs in southeastern Alaska and the presence of Abies (probably A. amabilis) indicate that precipitation was higher on eastern Graham Island during the mid-Wisconsin than at present.