Kinematic link between episodic trapdoor collapse of the Negra Muerta Caldera and motion on the Olacapato-El Toro Fault Zone, southern central Andes     

Juliane Ramelow  Ulrich Riller  Rolf L. Romer  Onno Oncken 《International Journal of Earth Sciences》2006,95(3):529-541

A combined geochronological and structural analysis of the Miocene Negra Muerta Caldera was designed to better understand caldera formation associated with prominent faults on the central Andean plateau. Rb–Sr ages of the caldera outflow facies indicate that caldera formation occurred in two volcano-tectonic episodes. The first episode commenced with explosive eruption of the 9.0±0.1 Ma andesitic Acay Ignimbrite followed by a period of volcanic quiescence and moderate tectonic activity. Dominant volcanic and tectonic activity occurred during the second episode, which is bracketed by eruption of the 7.6±0.1 Ma rhyolitic Toba 1 Ignimbrite and effusive discharge of the 7.3±0.1 Ma rhyodacitic to andesitic lava flows. Structural relationships between rocks of the Negra Muerta Volcanic Complex and collapse-induced normal faults, notably NE-striking normal faults, agree with simultaneous volcanic activity and floor subsidence of the caldera during the second episode. Floor subsidence was achieved by tilting on an outward dipping reverse fault to the northwest of the caldera floor around a hinge zone located south of the caldera floor. This induced horizontal extension of the caldera floor and was accomplished by fragmentation of, and intrusion of dikes into, the floor. Collapse-induced and post-collapse fault populations of the caldera do not differ significantly in the directions of their axes of maximum extension and are in this respect kinematically compatible with left-lateral slip on the nearby Olacapato-El Toro Fault Zone. This furnishes evidence for a kinematic control by prominent faults on the formation of collapse calderas in the central Andes. The structural analysis of the Negra Muerta Caldera shows that collapse calderas can serve as deformation markers that contribute in elucidating the regional kinematic regime and the time of activity of prominent dislocations genetically related to collapse calderas.  相似文献   

Recent ecological responses to climate variability and human impacts in the Nianbaoyeze Mountains (eastern Tibetan Plateau) inferred from pollen,diatom and tree-ring data   总被引：1，自引：0，他引：1  

Juliane Wischnewski  Ulrike Herzschuh  Kathleen M. Rühland  Achim Bräuning  Steffen Mischke  John P. Smol  Lily Wang 《Journal of Paleolimnology》2014,51(2):287-302

The Tibetan Plateau is a region that is highly sensitive to recent global warming, but the complexity and heterogeneity of its mountainous landscape can result in variable responses. In addition, the scarcity and brevity of regional instrumental and palaeoecological records still hamper our understanding of past and present patterns of environmental change. To investigate how the remote, high-alpine environments of the Nianbaoyeze Mountains, eastern Tibetan Plateau, are affected by climate change and human activity over the last ~600 years, we compared regional tree-ring studies with pollen and diatom remains archived in the dated sediments of Dongerwuka Lake (33.22°N, 101.12°E, 4,307 m a.s.l.). In agreement with previous studies from the eastern Tibetan Plateau, a strong coherence between our two juniper-based tree-ring chronologies from the Nianbaoyeze and the Anemaqin Mountains was observed, with pronounced cyclical variations in summer temperature reconstructions. A positive directional trend to warmer summer temperatures in the most recent decades, was, however, not observed in the tree-ring record. Likewise, our pollen and diatom spectra showed minimal change over the investigated time period. Although modest, the most notable change in the diatom relative abundances was a subtle decrease in the dominant planktonic Cyclotella ocellata and a concurrent increase in small, benthic fragilarioid taxa in the ~1820s, suggesting higher ecosystem variability. The pollen record subtly indicates three periods of increased cattle grazing activity (~1400–1480 AD, ~1630–1760 AD, after 1850 AD), but shows generally no significant vegetation changes during past ~600 years. The minimal changes observed in the tree-ring, diatom and pollen records are consistent with the presence of localised cooling centres that are evident in instrumental and tree-ring data within the southeastern and eastern Tibetan Plateau. Given the minor changes in regional temperature records, our complacent palaeoecological profiles suggest that climatically induced ecological thresholds have not yet been crossed in the Nianbaoyeze Mountains region.  相似文献   

Variability and alterations of water temperatures across the Elbe and Danube River Basins     

Danijela Markovic  Ulrike Scharfenberger  Stefan Schmutz  Florian Pletterbauer  Christian Wolter 《Climatic change》2013,119(2):375-389

Climate change is predicted to be a major threat to river ecosystems in the 21st century, but long-term records of water temperature in streams and rivers are rare. This study uses long-term water temperature series from the Elbe and the Danube River Basin to quantify the variability, magnitude, and extent of temperature alterations at different time scales. The observed patterns in monthly and daily water temperatures have been successfully described through statistical models based on air temperature, river discharge and the North Atlantic Oscillation Index. These models reveal that air temperature variability describes more than 80 % of the total water-temperature variability, linking anticipated changes in water temperature mainly to those in air temperature. The North Atlantic Oscillation effect deteriorates with decreasing latitude, while the discharge effect becomes more important and increases with the increase in discharge amount. The detected water temperature alterations include a phase shift in spring warming of almost 2 weeks, an increase in the number of days with temperatures above 25 °C and an increase in the duration of summer heat stress. These findings underline a significant risk for fundamental changes in river ecosystems, specifically in disruption of established patterns in food-web synchrony, and may lead to significant distortions in community structure and composition.  相似文献   

Assessing rheological properties of fluid mud samples through tuning fork data     

Fonseca  Diego Luiz  Marroig  Patrícia Cunha  Carneiro  Juliane Castro  Gallo  Marcos Nicolás  Vinzón  Susana Beatriz 《Ocean Dynamics》2019,69(1):51-57

Ocean Dynamics - At the nautical bottom approach, part of the fluid mud layers can be included in the available depth if they present favorable rheology. As it is difficult to perform in situ...  相似文献   

Rock slope failure in a recently deglaciated permafrost rock wall at Piz Kesch (Eastern Swiss Alps), February 2014          下载免费PDF全文

Marcia Phillips  Andrea Wolter  Rachel Lüthi  Florian Amann  Robert Kenner  Yves Bühler 《地球表面变化过程与地形》2017,42(3):426-438

In February 2014, a rock pillar with a volume of around 150 000  m³ collapsed at Piz Kesch in the Eastern Swiss Alps. A reconstruction of the conditions prior to the event and of the event itself is presented on the basis of different sources of data. The methods applied include photogrammetry, terrestrial laser scanning, structural geological analysis, examination of meteorological data, carbon‐14 (¹⁴C) dating of organic material in permafrost ice from a tension crack and numerical modelling of likely modes of failure. Despite a complete lack of in situ measurements in the rock wall prior to the event and of direct observations during the event, the available data allow the determination of the approximate timing of the event as well as the structural predisposition, the probable mode of failure and the timescale of several millennia involved in the triggering of the failure of the rock pillar. The interdisciplinary analysis of this event contributes towards understanding the complex interaction of processes involved in large rock slope failures currently occurring in warming mountain permafrost regions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Insights into Holocene relative sea-level changes in the southern North Sea using an improved microfauna-based transfer function     

Juliane Scheder  Friederike Bungenstock  Kristin Haynert  Anna Pint  Frank Schlütz  Peter Frenzel  Achim Wehrmann  Helmut Brückner  Max Engel 《第四纪科学杂志》2022,37(1):71-85

In light of global warming and rising relative sea level (RSL), detailed reconstructions of RSL histories and their controlling processes are essential in order to manage coastal-protection challenges. This study contributes to unravelling Holocene RSL change on the East Frisian North Sea coast in high resolution and with a new approach for the German Bight. For the first time, a transfer function (vertical error: 29.7 cm ? ~11% of the mean tidal range) for RSL change based on a combined training set of benthic foraminifers and ostracods from the back-barrier tidal basin of Spiekeroog is applied to the Holocene record of the back-barrier tidal basin of Norderney. The resulting RSL curve for the Norderney tidal basin is corrected for decompaction and shows a deceleration in RSL rise between 6000 and 5000 cal bp. The smallest possible error envelope (~1 m) results from the good suitability of salt-marsh layers between 5000 and 4000 cal bp. The RSL curve provides an approach towards the closure of the common data gap of peat-based curves for the southern North Sea related to a lack of basal peats in the youngest age range, and verifies regional differences in glacial isostatic adjustment.  相似文献