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62.
Elodie Lebas Sebastian Krastel Bernd Wagner Raphael Gromig Grigory Fedorov Marlene Baumer Natalia Kostromina Haflidi Haflidason 《Boreas: An International Journal of Quaternary Research》2019,48(2):470-487
A multi‐channel, high‐resolution seismic reflection survey using a Micro‐GI airgun was carried out in the framework of the Russian‐German project PLOT (Paleolimnological Transect) on Lake Levinson‐Lessing, Taymyr Peninsula, in 2016. In total, ~70 km of seismic reflection profiles revealed in unprecedented detail the glacial and postglacial sedimentary infill of the lake basin. Five main seismic units have been recognized and interpreted as glacial (Unit V), subglacial and proglacial (Unit IV), marine (Unit III), fluvial‐lacustrine (Unit II) and lacustrine (Unit I) sediments. Of particular significance are imbricated, south‐orientated structures present in the southernmost part of the lake basin within Unit V and a large topographic ridge recognized in front of those structures. We interpret these structures as push moraines and an end moraine, respectively, left by the glacier after its retreat. The depositional pattern of the units above the moraines documents past lake‐level fluctuations. We interpret Unit IV, Unit III and Unit I as highstand deposits, and Unit II as lowstand deposits. Gas‐charged sediments dominate the northern part of the lake basin, whilst they occur only sporadically and in limited spatial extent in the central and southern parts of the lake. In the latter areas, the seismic and echo‐sounder data suggest recent tectonic activity. Our study contributes to the reconstruction of environmental conditions in the Taymyr Peninsula directly following the Early Weichselian deglaciation and shows that deep tectonic lake basins affected by several glaciations can preserve important palaeoenvironmental records, which contributes significantly to our understanding of palaeoenvironmental changes in the Taymyr Peninsula and the central Russian Arctic. 相似文献
63.
Raphael Gromig Bernd Wagner Volker Wennrich Grigory Fedorov Larisa Savelieva Elodie Lebas Sebastian Krastel Dominik Brill Andrei Andreev Dmitry Subetto Martin Melles 《Boreas: An International Journal of Quaternary Research》2019,48(2):330-348
Lake Ladoga in northwestern Russia is Europe's largest lake. The postglacial history of the Ladoga basin is for the first time documented continuously with high temporal resolution in the upper 13.3 m of a sediment core (Co1309) from the northwestern part of the lake. We applied a multiproxy approach including radiographic imaging, (bio‐)geochemical and granulometric analyses. Age control was established combining radiocarbon dating with varve chronology, the latter anchored to a correlated radiocarbon age from a lake close by. The age‐depth model reveals the onset of glacial varve sedimentation at 13 910±140 cal. a BP, when Lake Ladoga was part of the Baltic Ice Lake. Linear extrapolation of published retreat rates of the Scandinavian Ice Sheet provides a formation age of the Luga moraine close to Lake Ladoga's southern shore of 14.5–15.9 cal. ka BP, older than previously assumed. Varve sedimentation covers the Bølling/Allerød interstadial, the Younger Dryas stadial and the Early Holocene. Varve‐thickness variations, conjoined with grain‐size and geochemical variations, inform about the relative position of the Scandinavian Ice Sheet and the climate during the deglaciation phase. The upper limit of the varved succession marks the change from glaciolacustrine to normal lacustrine sedimentation and post‐dates the drainage of the Baltic Ice Lake as well as the formation of the Salpausselkä II moraine north of Lake Ladoga, by c. 250 years. The Holocene sediment record is divided into three periods in the following order: (i) a lower transition zone between the Holocene boundary and c. 9.5 cal. ka BP, characterized by mostly massive sediments with low organic content, (ii) a phase with increased organic content from c. 9.5 to 4.5 cal. ka BP corresponding to the Holocene Thermal Maximum, and (iii) a phase with relatively stable sedimentation in a lacustrine environment from c. 4.5 cal. ka BP until present. 相似文献
64.
Riverbank erosion is an important component of catchment sediment budget models but remains one of the least well-understood processes, particularly at large spatial scales. Here, we develop and test a new bank migration model in New Zealand for large catchment applications that (1) better represents spatial variability in factors influencing bank erosion and (2) improves predictive performance. We represent bank migration rates as a function of reach-scale stream power, channel sinuosity, soil texture, valley confinement, riparian woody vegetation and channel protection works. The new model significantly improves prediction compared to the SedNetNZ model. Comparison of measured bank migration rates with individual variables shows percent silt + clay derived from soil maps exhibited the strongest correlation, whereas other variables were non-significant. The model results demonstrate that improved prediction can be achieved by combining spatial representation of multiple factors over large areas, despite low correlation between individual variables and bank migration rates. 相似文献
65.
Anthony Raphael Davidson William Rayment Steve M Dawson Trudi Webster Elisabeth Slooten 《新西兰海洋与淡水研究杂志》2018,52(3):372-382
Southern right whales (Eubalaena australis) were widespread in New Zealand waters before commercial whaling in the nineteenth century caused drastic declines in their abundance and distribution. Following the cessation of whaling, the population has been recovering and is now slowly recolonising its former range. Estimates of population demographics, including reproductive output, are essential for predicting the trajectory of this population. We gathered photo-identification data on female southern right whales during annual field trips to the Auckland Islands, the principal calving area in New Zealand waters. Forty-five calving intervals were observed between 2006 and 2013 (mean interval?=?3.31 years, 95% CI?=?3.06–3.57). Incorporating the effects of possible missed calving events produced a plausible range of mean calving intervals from 3.17 to 3.31 years. Our results suggest that the calving interval of New Zealand southern right whales is similar to that found in populations elsewhere. 相似文献
66.
Lynch's Crater on the Atherton Tablelands in NE-Australia formed about 230,000 years ago during an explosive eruption, creating a maar more than 80 m deep. Since the eruption, the maar has been filled with lake sediments that are topped by peat material. A 64 m long core was recovered and an OSL dating project was undertaken to extend the chronology beyond 16 m depth, which according to 14C age control represents ~60 ka. The predominantly organic lake sediments contained abundant fine quartz of aeolian origin, and the Single Aliquot Regenerative Method (SAR) provided satisfactory equivalent dose (DE) estimates. However, the determination of the dose rate proved both critical and difficult. Extremely low radionuclide contents led to cosmic radiation being the dominant dose rate contribution for most samples. The OSL chronology presented in this paper thus relies on modelling the changing cover by sediments and lake water over the burial time. 相似文献
67.
Nevado del Huila, a glacier-covered volcano in the South of Colombia’s Cordillera Central, had not experienced any historical
eruptions before 2007. In 2007 and 2008, the volcano erupted with phreatic and phreatomagmatic events which produced lahars
with flow volumes of up to about 300 million m3 causing severe damage to infrastructure and loss of lives. The magnitude of these lahars and the prevailing potential for
similar or even larger events, poses significant hazards to local people and makes appropriate modeling a real challenge.
In this study, we analyze the recent lahars to better understand the main processes and then model possible scenarios for
future events. We used lahar inundation depths, travel duration, and flow deposits to constrain the dimensions of the 2007
event and applied LAHARZ and FLO-2D for lahar modeling. Measured hydrographs, geophone seismic sensor data and calculated
peak discharges served as input data for the reconstruction of flow hydrographs and for calibration of the models. For model
validation, results were compared with field data collected along the Páez and Simbola Rivers. Based on the results of the
2007 lahar simulation, we modeled lahar scenarios with volumes between 300 million and 1 billion m3. The approach presented here represents a feasible solution for modeling high-magnitude flows like lahars and allows an assessment
of potential future events and related consequences for population centers downstream of Nevado del Huila. 相似文献
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70.
The Transfiguration Cu–Pb–Zn–Ag deposit, enclosed within reduced grey sandstone, is associated with continental red beds of
the Lower Silurian Robitaille Formation in the Quebec Appalachians, Canada. The Robitaille Formation rests unconformably on
foliated Cambro-Ordovician rocks. The unconformity is locally cut by barite veins. The basal unit of the Robitaille Formation
comprises green wacke and pebble conglomerate, which locally contain calcite nodules. The latter have microstructures characteristic
of alpha-type calcretes, such as “floating” fabrics, calcite-filled fractures (crystallaria) and circumgranular cracks. Massive,
grey sandstone overlies the basal green wacke and pebble conglomerate unit, which is overlain, in turn, by red, fine-grained
sandstone. Mineralisation occurred underneath the red sandstone unit, chiefly in the grey sandstone unit, as disseminated
and veinlet sulphides. Chalcopyrite, the most abundant Cu sulphide, replaced early pyrite. Calcrete, disseminated carbonate
and vein carbonate have stable isotope ratios varying from −7.5‰ to −1.1‰ δ13C and from 14.7‰ to 21.3‰ δ18O. The negative δ13C values indicate the oxidation of organic matter in a continental environment. Sulphur isotope ratios for pyrite, chalcopyrite
and galena vary from −19‰ to 25‰ δ34S, as measured on mineral concentrates by a conventional SO2 technique. Laser-assisted microanalyses (by fluorination) of S isotopes in pyrite show an analogous range in δ34S values, from −21‰ to 25‰. Negative and positive δ34S values are compatible with bacterial sulphate reduction (BSR) in systems open and closed with respect to sulphate. We interpret
similarly high δ34S values for sulphide concentrates (25.1‰) and for vein barite (26.2‰) to result from rapid and complete thermochemical reduction
of pore-water sulphate. Two early to late diagenetic stages of mineralisation best explain the origin of the Transfiguration
deposit. The first stage was characterised by the ponding of groundwater over the Taconian unconformity, recorded by calcrete
and early pyrite formation via BSR in grey sandstone. Early pyrite contains up to 2 wt.% Pb, which is consistent with Pb fixation
by sulphate-reducing bacteria. The second stage (II) is defined by the replacement of early pyrite by chalcopyrite, as well
as by sulphide precipitation via either BSR or thermochemical sulphate reduction (TSR) in grey sandstone. This event resulted
from the synsedimentary fault-controlled percolation and mixing of (1) an oxidising, sulphate-bearing cupriferous fluid migrating
per descensum from the red-bed sequence and (2) a hydrocarbon-bearing fluid migrating per ascensum from the Cambro-Ordovician basement. Mixing between the two fluids led to sulphate reduction, causing Cu sulphide precipitation.
The positive correlation between Cu and Fe3+/Fe2+ bulk rock values suggests that Fe acted as a redox agent during sulphate reduction. Stage II diagenetic fluid migration is
tentatively attributed to the Late Silurian Salinic extensional event. 相似文献