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31.
Lorena Rebolledo Julio Sepúlveda Carina B. Lange Silvio Pantoja Sébastien Bertrand Konrad Hughen Dante Figueroa 《Estuarine, Coastal and Shelf Science》2008
A multi-proxy approach based on organic (organic carbon, alkenones, and C/N) and inorganic geochemical proxies (biogenic opal, inorganic carbon, Fe, Ti, and Ca) preserved in the sediments of the Jacaf channel (CF7-PC33; 44°21′S, 72°58′W, 510 m water depth), Chilean fjords, yields evidence of major past productivity fluctuations in accordance with climatic changes over the last ∼1800 years. The downcore record clearly shows two productivity/climate modes. The first period, prior to 900 cal yr BP, is characterized by decreased marine productivity and a reduced continental signal, pointing to diminished precipitation and runoff. In contrast, the second period between ∼750 cal yr BP and the late 1800s (top of core) is illustrated by elevated productivity and an increased continental signal, suggesting higher precipitation and runoff. Both time intervals are separated by a relatively abrupt transition of ∼150 years which roughly coincides with the beginning of the Little Ice Age. The increased content of freshwater diatoms and Chrysophyte cysts that characterize the last 200 years of the latter mode coincides with a significant decrease in the carbonate content of the sediment; together they further indicate increased terrigenous contributions and decreased marine carbonate productivity at the end of the Little Ice Age. The correspondence between our record and other paleoclimate studies carried out in South America and Antarctica demonstrates that the Chilean fjord area of Northern Patagonia is not just sensitive to local climatic variability but also to regional and possibly global variability. 相似文献
32.
Lorena Ramos Marta Alperin Antje Schwalb Vera Markgraf Daniel Ariztegui Gabriela Cusminsky 《Boreas: An International Journal of Quaternary Research》2019,48(3):746-760
Changes in the ostracod assemblages from two sediment cores collected from Lago Cardiel in southeastern Patagonia (49°S) reflect the main regional abrupt climatic changes over the last 15.6 cal. ka BP. Shifts in species abundance and switches in dominances suggest that these were mainly driven by variable salinity. During the Late Pleistocene, Limnocythere rionegroensis was abundant and dominant, indicating waters with high salinity and prevalence of evaporative processes. Between 12.6 and 10.8 cal. ka BP, Lago Cardiel expanded markedly and reached an Early Holocene highstand of +55 m above present lake level. A major change in ostracod assemblage in which Limnocythere patagonica appears as the dominant species in parallel with the disappearance of L. rionegroensis and Eucypris aff. cecryphalium mirrored this transitional period between the cold and dry Late Pleistocene and the humid and warm Early Holocene. Over the last 4 cal. ka BP, L. rionegroensis returned to the species assemblage and Riocypris whatleyi increased its abundance pointing towards increasing salinities. The variations in size, shape and ornamentation of L. rionegroensis and R. whatleyi fossil valves were examined using geometric morphometric techniques and further compared to those of modern Patagonian sites. Limnocythere rionegroensis specimens displayed high morphological variability during the evolution of Lago Cardiel. More specifically, the switch in reproductive mode – from sexual to parthenogenetic– and the increase in valve ornamentation around 12.7 cal. ka BP suggest that these changes were promoted by the hydrological alteration that occurred in the Late Pleistocene. This exercise provides a robust range of morphological variation for these proxies, which will be useful in further taxonomic and palaeoenvironmental studies adding more information about different factors influencing the observed morphological trends. 相似文献
33.
Lorena Grana Pablo Tchilinguirian Salomn Hocsman Patricia Escola Nora I. Maidana 《Geoarchaeology》2016,31(5):412-433
This article focuses on local paleohydrological changes experienced by the Las Pitas and Miriguaca Rivers in the south‐central Andes of Argentina and their impacts on hunter‐gatherers as they transitioned to food‐producing communities 7000–3000 cal. yr B.P. Paleoenvironmental reconstruction based on geomorphology, alluvial sedimentology, and diatom evidence indicates a dry phase of reduced streamflow between ca. 6700 and 4800 cal. yr B.P. for the Las Pitas River, and 6600 and 3000 cal. yr B.P. for the Miriguaca River. A phase of more humid environmental conditions commenced after ca. 4900 cal. yr B.P. along the Las Pitas River, and after 3000 cal. yr B.P. along the Miriguaca River. Differences in the chronology and magnitude of hydrological changes along both rivers are related to topographic and hydrological characteristics of their respective watersheds. Higher catchment elevation and enhanced orographic precipitation favored greater sensitivity for the Las Pitas River to short humid events during the middle‐to‐late Holocene. The archaeological evidence suggests that the paleohydrological changes within these catchments played a significant role in human occupational dynamics such that the Las Pitas River offered better environmental conditions for human occupation relative to the Miriguaca River as foragers increasingly relied on plant and animal domestication. 相似文献
34.
Martín Hernández-Marín Lilia Guerrero-Martínez Alfredo Zermeño-Villalobos Lorena Rodríguez-González Thomas J. Burbey Jesús Pacheco-Martínez Sergio I. Martínez-Martínez Norma González-Cervantes 《Hydrogeology Journal》2018,26(8):2811-2826
The investigation involves a temporal and spatial analysis to characterize recharge in the Aguascalientes valley in central Mexico. The results are based on a two-part methodological strategy using a geospatial and numerical analysis. Results from the geospatial analysis are based on the analytical hierarchical process (AHP) method, which involves developing a zoning map that qualifies the conditions for groundwater recharge in the valley. In addition, one-dimensional numerical modeling based on the van Genuchten equation was applied for various soil column configurations to estimate the transit time of recharge through the vadose zone. The analysis was performed over a 20-year period from 1995 to 2015. The results of the geospatial analysis indicate that the optimal area for groundwater recharge is the lower zone of the valley, particularly the portion influenced by surface discontinuities. The shortest estimated period of recharge for water to pass through the vadose zone is approximately 4.25 years. 相似文献
35.
Alessandro?Zini Sergio?GrausoEmail author Vladimiro?Verrubbi Luca?Falconi Gabriele?Leoni Claudio?Puglisi 《Landslides》2015,12(5):847-859
Debris flows represent dangerous occurrences in many parts of the world. Several disasters are documented due to this type of fast-moving landslides; therefore, natural-hazard assessment of debris flows is crucial for safety of life and property. To this aim, much current work is being directed toward developing geotechnical-hydraulic models for the evaluation of debris flow susceptibility. A common base for such current models is parameterization of background predisposing and triggering factors such as inherent characteristics of geo-materials, topography, landscape and vegetation cover, rainfall regime, human activities, etc. which influence the occurrence of these processes on slopes. The same factors are also taken into account in soil erosion prediction models. Consequently, it seems worth investigating the effectiveness of the soil erosion index as debris flows susceptibility indicator. To this aim, a logistic regression analysis was carried out between the erosion index assessed by means of the Revised Universal Soil Loss Equation (RUSLE) model and the inventory of debris flows that have occurred in an area in Sicily (Southern Italy). Model assumptions were verified and validated by means of a series of statistical tools. Different possible scenarios were also evaluated by considering hypothetical changes in soil erosion rate under different rain erosivity conditions. Notwithstanding the rough approximations in model data collection, the outcomes appear encouraging. 相似文献
36.
Surendra P. Verma Lorena Díaz-González John S. Armstrong-Altrin 《Earth Science Informatics》2016,9(2):151-165
TecSand is a new Java software that is used for deciphering the tectonic setting of clastic sediments and sedimentary rocks through two new multidimensional discrimination diagrams. For each sample, TecSand calculates four complex discriminant functions: DF1m1 and DF2m1 for the high-silica diagram and DF1m2 and DF2m2 for the low-silica diagram, each representing linear combinations of log-ratios of all major elements. These functions determine the position of each sample within island or continental arc, continental rift, and collision/convergent settings. The program also calculates the probability values for the three tectonic fields. TecSand provides a “ready for publication” report for each locality, including the adjusted major elements, log-transformed variables, DF1 and DF2 results, and probability values for individual samples. Validations from samples of known tectonic settings, evaluation of chemical changes, and applications to Precambrian clastic sediments have previously been demonstrated in the literature. Therefore, we illustrate the use of TecSand in 10 case studies covering ages from the Early Cambrian to the Holocene. The results obtained from these two diagrams were not only mutually consistent but also with other geological constraints. As an innovation, TecSand provides an overall synthesis of the two diagrams as total percent probability values. Comparison of the results of this study with the previously published tectonic discrimination diagrams reveals that two recent multidimensional discrimination diagrams are more efficient in discriminating tectonic settings. Although TecSand does provide graphics, which can be imported and modified in commercial software, plotting of the sample diagram is no longer required. 相似文献
37.
Surendra P. Verma Lorena Díaz-González Javier A. Pérez-Garza Mauricio Rosales-Rivera 《Arabian Journal of Geosciences》2016,9(20):740
Data quality control in geochemistry constitutes a fundamental problem that is still to be solved from the application of statistics and computation. We used refined Monte Carlo simulations of 10,000 replications and 190 independent experiments for sample sizes of 5 to 100. Statistical contaminations of 1 to 4 observations were used to compare 9 statistical parameters (4 central tendency—mean, median, trimean, and Gastwirth mean, and 5 dispersion estimates—standard deviation, median absolute deviation, S n , Q n , and \( {\widehat{\sigma}}_n \)). The presence of discordant observations in the data arrays rendered the outlier-based and robust parameters to disagree with each other. However, when the mean and standard deviation (outlier-based parameters) were estimated from censored data arrays obtained after the identification and separation of outlying observations, they generally provided a better estimate of the population than the robust estimates obtained from the original data arrays. This inference is contrary to the general belief, and therefore, reasons for the better performance of the outlier-based methods as compared to the robust methods are suggested. However, when all parameters were estimated from censored arrays and appropriate precise and accurate correction factors put forth in this work were applied, all of them became fully consistent, i.e., the mean agreed with the median, trimean and Gastwirth mean, and the standard deviation with the median absolute deviation, S n , Q n , and \( {\widehat{\sigma}}_n \). An example of inter-laboratory chemical data for a Hawaiian reference material BHVO-1 included sample sizes from 5 to 100, which showed that small samples of up to 20 provide inconsistent estimates, whereas larger samples of 20–100, especially >40, were more appropriate for estimating statistical parameters through robust or outlier-based methods. Although all statistical estimators provided consistent results, our simulation study shows that it is better to use the censored sample mean and population standard deviation as the best estimates. 相似文献
38.
This paper delineates our use of 10 708 km2 of three‐dimensional (3D) seismic data from the continental margin of Trinidad and Tobago West Indies to describe a series of mass transport complexes (MTCs) that were deposited during the Plio‐Pleistocene. This area, situated along the obliquely converging boundary of the Caribbean/South American plates and proximal to the Orinoco Delta, is characterized by catastrophic shelf‐margin processes, intrusive/extrusive mobile shales and active tectonism. Extensive mapping of different stratigraphic intervals of the 3D seismic survey reveals several MTCs that range in area from 11.3 to 2017 km2. Three types of MTCs are identified: (1) shelf‐attached systems that were fed by shelf‐edge deltas whose sediment input is controlled by sea‐level fluctuations and sedimentation rates; (2) slope‐attached systems, which occur when upper‐slope sediments catastrophically fail owing to gas‐hydrate disruptions and/or earthquakes and (3) locally detached systems, formed when local instabilities in the seafloor trigger relatively small collapses. Such classification of the relationship between slope mass failures and sourcing regions enables a better understanding of the nature of initiation, length of development history and petrography of such MTCs. 3D seismic enables more accurate calculation of deposit volumes, improves deposit imaging, and, thus, increases the accuracy of physical and computer simulations of mass failure processes. 相似文献
39.
Digital technologies, including participatory Internet mapping, social media and smartphones, provide new avenues for research in outdoor recreation and tourism. The potential to reach a greater audience and collect visitation data on a broader scale, with less costs than traditional paper surveys, are key advantages that have increased the use of these novel technologies. Using of mobile apps for data collection is still at the experimental stage. We evaluate previous attempts to use apps for monitoring recreation and tourism in protected areas, as an alternative to other in situ or online methods. We present a pilot study implemented in Jotunheimen National Park (Norway), where we developed a mobile app for visitor monitoring and real-time mapping of values and experiences. We present the lessons learned, give suggestions on how and for what apps can be used, and discuss the advantages and limitations of using smartphones for visitor monitoring in protected areas. 相似文献
40.
The objective of this study was to better understand the linkages between spatial patterns of forest use, land use, and rates of deforestation. We focused on a region of the Brazilian Amazon characterized by a variety of spatial patterns of deforestation and that experienced rapid deforestation in the last decade: the colonization project “Pedro Peixoto” in the extreme East of Acre State. By combining time series of remote sensing data and household survey data, we tested the hypothesis that each spatial pattern of deforestation is associated with specific socio-economic characteristics of land managers. The statistical results support our hypothesis. However, spatial patterns of deforestation are not a consequence of the main economic activities. Rather, spatial patterns of forest use are linked to the pre-conceived design of the settlement project. The main economic activities are influenced by factors such as the property size, their location and disposition, and the availability of infrastructure. 相似文献