Seismic evidence of up to 200 m lake‐level change in Southern Patagonia since Marine Isotope Stage 4     

ANDREA CATALINA GEBHARDT  CHRISTIAN OHLENDORF  FRANK NIESSEN  MARC DE BATIST  FLAVIO S. ANSELMETTI  DANIEL ARIZTEGUI  PIERRE KLIEM  STEFAN WASTEGÅRD  BERND ZOLITSCHKA 《Sedimentology》2012,59(3):1087-1100

Maar lake Laguna Potrok Aike is located north of the Strait of Magellan (south‐eastern Patagonia). Seismic reflection profiles revealed a highly dynamic palaeoclimate history. Dunes were identified in the eastern part of the lake at approximately 30 to 80 m below the lake floor, overlying older lacustrine strata, and suggest that the region experienced dry conditions probably combined with strong westerly winds. It is quite likely that this can be linked to a major dust event recorded in the Antarctic ice cores during Marine Isotope Stage 4. The dunes are overlain by a series of palaeo‐shorelines indicating a stepwise water‐level evolution of a new lake established after this dry period, and thus a change towards wetter conditions. After the initial, rapid and stepwise lake‐level rise, the basin became deeper and wider, and sediments deposited on the lake shoulder at approximately 33 m below present‐day lake level point towards a long period of lake‐level highstand between roughly 53·5 ka cal. bp and 30 ka cal. bp with a maximum lake level some 200 m higher than the desiccation horizon. This highstand was then followed by a regressional phase of uncertain age, although it must have happened some time between approximately 30 ka cal. bp and 6750 yrs cal. bp . Dryer conditions during the Mid‐Holocene are evidenced by a dropping lake level, resulting in a basin‐wide erosional unconformity on the lake shoulder. A second stepwise transgression between ca 5·8 to 5·4 ka cal. bp and ca 4·7 to 4 ka cal. bp with palaeo‐shorelines deposited on the lake shoulder unconformity again indicates a change towards wetter conditions.  相似文献   

DORIS-DIODE: Jason-1 has a Navigator on Board     

CHRISTIAN JAYLES  PATRICK VINCENT  FABIEN ROZO  FABIEN BALANDREAUD 《Marine Geodesy》2013,36(3-4):753-771

DIODE (Doris Immediate On-board orbit DEtermination) is a series of real-time orbit determination software, which process one-way up-link Doppler measurements performed by a DORIS receiver on a satellite. The DIODE software are embedded within the DORIS receivers, and they provide orbit and time determination to the user as well as technical parameters to adjust the tracking loop within the instrument. After a first successful flight on-board SPOT4, the second generation of the family operates on-board Jason-1, with more efficient and more accurate algorithms. Similar versions have been embarked onboard SPOT5 and ENVISAT. The accuracy is between 10 and 30 centimeters RMS for the radial component, and about 50 centimeters RMS in 3D. With several Failure Detection and Incident Recovery (FDIR) enhancements implemented in the software, DIODE/Jason-1 has experienced only one anomaly in July 2004; its availability is 99.7%, after two years and a half in-orbit. This article describes the DORIS/DIODE element of the Jason-1 system. It summarizes the main results obtained from the various verification activities that concerned all parts of this navigation and time-tagging Jason-1 subsystem.  相似文献   

Anatomy of a subaqueous ice-contact fan and delta complex, Middle Pleistocene, North-west Germany     

JUTTA WINSEMANN  JAHN J. HORNUNG  JANINE MEINSEN  ULRICH ASPRION  ULRICH POLOM†  CHRISTIAN BRANDES  MICHAEL BUßMANN  CHRISTIAN WEBER 《Sedimentology》2009,56(4):1041-1076

This paper presents a detailed analysis of the high‐resolution facies architecture of the Middle Pleistocene Porta subaqueous ice‐contact fan and delta complex, deposited on the northern margin of glacial Lake Weser (North‐west Germany). A total of 10 sand and gravel pits and more than 100 wells were examined to document the complex facies architecture. The field study was supplemented with a ground‐penetrating radar survey and a shear‐wave seismic survey. All collected sedimentological and geophysical data were integrated into a high‐resolution three‐dimensional geological model for reconstructing the spatial distribution of facies associations. The Porta subaqueous fan and delta complex consist of three fan bodies deposited on a flat lake‐bottom surface at the margin of a retreating ice lobe. The northernmost fan complex is up to 55 m thick, 6·2 km wide and 6·5 km long. The incipient fan deposition is characterized by high‐energy flows of a plane‐wall jet. Very coarse‐grained, highly scoured jet‐efflux deposits with an elongate plan shape indicate a high Froude number, probably >5. These jet‐efflux sediments are deposited in front of a large ～3·2 km long, up to 1·2 km wide, and up to 25 m deep flute‐like scour, indicating the most proximal erosion and bypass area of the jet that widens and deepens with distance downstream to the region of maximum turbulence (approximately five times the conduit diameter). Evidence for subsequent flow splitting is given by the presence of two marginal gravel fan lobes, deposited in front of 1·3 to 2·5 km long flute‐like scours, that are 0·8 to 1 km wide and 7 to 20 m deep. In response to continued aggradation, small jets developed at the periphery of these bar‐like deposits and filled in the low areas adjacent to the original superelevated regions, locally raising the depositional surface and characterized by large‐scale trough cross‐stratified sand and pebbly sand. The incision of an up to 1·2 km wide and up to 35 m deep channel into the evolving fan is attributed to a catastrophic drainage event, probably related to a lake outburst and lake‐level fall in the range of 40 to 60 m. At the mouth of this channel, highly scoured jet‐efflux deposits formed under hydraulic‐jump conditions during flow expansion. Subsequently, Gilbert‐type deltas formed on the truncated fan margin, recording a second lake‐level drop in the range of 30 to 40 m. These catastrophic lake‐level falls were probably caused by rapid ice‐lobe retreat controlled by the convex‐up bottom topography of the ice valley.  相似文献   

Environmental history of southern Patagonia unravelled by the seismic stratigraphy of Laguna Potrok Aike     

FLAVIO S. ANSELMETTI  DANIEL ARIZTEGUI†  MARC DE BATIST‡  A. CATALINA GEBHARDT§  TORSTEN HABERZETTL¶  FRANK NIESSEN§  CHRISTIAN OHLENDORF  BERND ZOLITSCHKA 《Sedimentology》2009,56(4):873-892

Laguna Potrok Aike, located in southernmost Patagonia (Argentina, 52°S) is a 100 m deep hydrologically closed lake that probably provides the only continental southern Patagonian archive covering a long and continuous interval of several glacial to interglacial cycles. In the context of the planned ‘International Continental Scientific Drilling Program’ initiative ‘Potrok Aike Maar Lake Sediment Archive Drilling Project’, several seismic site surveys that characterize in detail the sedimentary subsurface of the lake have been undertaken. Long sediment cores recovered the material to date and calibrate these seismic data. Laguna Potrok Aike is rimmed steeply, circular in shape with a diameter of ∼3·5 km and is surrounded by a series of subaerial palaeoshorelines, reflecting varying lake-level highstands and lowstands. Seismic data indicate a basinwide erosional unconformity that occurs consistently on the shoulder of the lake down to a depth of −33 m (below 2003 ad lake level), marking the lowest lake level during Late Glacial to Holocene times. Cores that penetrate this unconformity comprise Marine Isotope Stage 3-dated sediments (45 kyr bp ) ∼3·5 m below, and post-6800 cal yr bp transgressional sediments above the unconformity. This Middle Holocene transgression following an unprecedented lake-level lowstand marks the onset of a stepwise change in moisture, as shown by a series of up to 11 buried palaeoshorelines that were formed during lake-level stillstands at depths between −30 and −12 m. Two series of regressive shorelines between ∼5800 to 5400 and ∼4700 to 4000 cal yr bp interrupt the overall transgressional trend. In the basin, mound-like drift sediments occur after ∼6000 cal yr bp, documenting the onset of lake currents triggered by a latitudinal shift or an increase in wind intensity of the Southern Hemispheric Westerlies over Laguna Potrok Aike at that time. Furthermore, several well-defined lateral slides can be recognized. The majority of these slides occurred during the mid-Holocene lake-level lowering when the slopes became rapidly sediment-charged because of erosion from the exposed shoulder sediments. Around 7800 and 4900 cal yr bp , several slides went down simultaneously, probably triggered by seismic shaking.  相似文献   

Age of landslides along the Grande Rivière de la Baleine estuary, eastern coast of Hudson Bay, Québec (Canada)     

CHRISTIAN BÉGIN  LOUISE FILION 《Boreas: An International Journal of Quaternary Research》1988,17(3):289-299

A 12km long terrace along the estuary of the Grande Rivière de la Baleine, northern Québec (5517'N, 7747'W), has been locally modified by seven large landslides during the last 3,200¹⁴ C years. The oldest undated landslide occurred between 3,200 B.P(formation of the upper terrace) and 2,200B.P., i.e. the radio carbon age of the second oldest landslide. The third one occurred around 900B.P. sometime before peat started to accumulate on the flowbowl floor. The more recent landslides were dendrochronologically dated. They were formed in less than 30 years, i.e. in 1818 (2 synchronous landslides), 1839 and 1846 A.D. These 19th-century landslides were dated through a comparative analysis of growth curves derived from buried trees found in the flowing sediments or from tilted and cut trees, with the regional master chronologies and the northern Québec light-ring chronology, using more specifically the 1816 and 1817 light-ring years. The 1818 landslides occurred during the growing season (July), whereas the 1839 and 1846 landslides were formed during spring. The occurrence of numerous landslides during this short period seems to be related to sustained cool and humid climatic conditions that may have enhanced the subsoil water content.  相似文献   

Accuracy of discharge determined from a rating curve     

JOHN R. DYMOND  ROSS CHRISTIAN 《水文科学杂志》2013,58(4):493-504

ABSTRACT

An error analysis shows that three types of errors influence the random error of a single discharge measurement determined from a rating curve. They are rating curve error, water level measurement error and an error caused by ignoring all physical parameters, other than water level, that affect discharge. Methods in the literature for evaluating the first two types of errors are reviewed and a method for evaluating the third type is given. The error of average discharge for an arbitrary period is also considered.  相似文献   

A multi‐dating approach applied to proglacial sediments attributed to the Most Extensive Glaciation of the Swiss Alps     

ANDREAS DEHNERT  FRANK PREUSSER  JAN D. KRAMERS  NAKI AKÇAR  PETER W. KUBIK  REGINA REBER  CHRISTIAN SCHLÜCHTER 《Boreas: An International Journal of Quaternary Research》2010,39(3):620-632

Dehnert, A., Preusser, F., Kramers, J. D., Akçar, N., Kubik, P. W., Reber, R. & Schlüchter, C. 2010: A multi‐dating approach applied to proglacial sediments attributed to the Most Extensive Glaciation of the Swiss Alps. Boreas, Vol. 39, pp. 620–632. 10.1111/j.1502‐3885.2010.00146.x. ISSN 0300‐9483. The number and the timing of Quaternary glaciations of the Alps are poorly constrained and, in particular, the age of the Most Extensive Glaciation (MEG) in Switzerland remains controversial. This ice advance has previously been tentatively correlated with the Riss Glaciation of the classical alpine stratigraphy and with Marine Isotope Stage (MIS) 6 (186–127 ka). An alternative interpretation, based on pollen analysis and stratigraphic correlations, places the MEG further back in the Quaternary, with an age equivalent to MIS 12 (474–427 ka), or even older. To re‐evaluate this issue in the Swiss glaciation history, a multi‐dating approach was applied to proglacial deltaic ‘Höhenschotter’ deposits in locations outside the ice extent of the Last Glacial Maximum. Results of U/Th and luminescence dating suggest a correlation of the investigated deposits with MIS 6 and hence with the Riss Glaciation. Cosmogenic burial dating suffered from large measurement uncertainties and unusually high ²⁶Al/¹⁰Be ratios and did not provide robust age estimates.  相似文献   

36Cl production rate from K‐spallation in the European Alps (Chironico landslide,Switzerland)          下载免费PDF全文

JOERG M. SCHAEFER  AARON E. PUTNAM  TOBY KOFFMAN  LUCILLA BENEDETTI  SUSAN IVY‐OCHS  CHRISTIAN SCHLÜCHTER 《第四纪科学杂志》2014,29(5):407-413

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Litho- and chronostratigraphy of the Late Weichselian in Vendsyssel, northern Denmark, with special emphasis on tunnel-valley infill in relation to a receding ice margin     

CHARLOTTE FOG KROHN  NICOLAJ KROG LARSEN  CHRISTIAN KRONBORG  OLE BJØRSLEV NIELSEN  KAREN LUISE KNUDSEN 《Boreas: An International Journal of Quaternary Research》2009,38(4):811-833

Lithostratigraphy and chronostratigraphy of samples from 18 deep boreholes in Vendsyssel have resulted in new insight into the Late Weichselian glaciation history of northern Denmark. Prior to the Late Weichselian Main advance c. 23–21 kyr BP, Vendsyssel was part of an ice‐dammed lake where the Ribjerg Formation was deposited c. 27–23 kyr BP. The timing of the Late Weichselian deglaciation is well constrained by the Main advance and the Lateglacial marine inundation c. 18 kyr BP, and thus spans only a few millennia. Rapid deposition of more than 200 m of sediments took place mainly in a highly dynamic proglacial and ice‐marginal environment during the overall ice recession. Mean retreat rates have been estimated as 45–50 m/yr in Vendsyssel with significantly higher retreat rates between periods of standstill and re‐advance. The deglaciation commenced in Vendsyssel c. 20 kyr BP, and the Troldbjerg Formation was deposited c. 20–19 kyr BP in a large ice‐dammed lake in front of the receding ice sheet, partly as glaciolacustrine sediments and partly as rapid and focused sedimentation in prominent ice‐contact fans, which make up the Jyske Ås and Hammer Bakker moraines. In the northern part of central Vendsyssel, at least four generations of north–south orientated tunnel valleys are identified, each generation related to a recessional ice margin. This initial deglaciation was interrupted by a major re‐advance from the east c. 19 kyr BP, which covered most of Vendsyssel. An ice‐dammed lake formed in front of the ice sheet as it retreated towards the east; the Morild Formation was deposited here c. 19–18 kyr BP. Related to this stage of deglaciation, eight ice‐marginal positions have been identified based on the distribution of large tunnel‐valley systems and pronounced recessional moraines. The Morild Formation consists of glaciolacustrine sediments, including the sediment infill of more than 190 m deep tunnel valleys, as well as the sediments in recessional moraines, which were formed as ice‐contact sedimentary ridges, possibly in combination with glaciotectonic deformation. The character of the tunnel‐valley infill sediments was determined by proximity to the ice margin. During episodes of rapid retreat of the ice margin, tunnel valleys were quickly abandoned and filled with fine‐grained sediments in a distal setting. During slow retreat of the ice margin, tunnel valleys were filled in an ice‐proximal environment, and the infill consists of alternating layers of fine‐ to coarse‐grained sediments. At c. 18 kyr BP, Vendsyssel was inundated by the sea, when the Norwegian Channel Ice Stream broke up, and a succession of marine sediments (Vendsyssel Formation) was deposited during a forced regression.  相似文献   

Late Pleistocene glacial history of Jameson Land, central East Greenland, derived from cosmogenic ¹⁰Be and ²⁶Al exposure dating     

LENA HÅKANSSON  HELENA ALEXANDERSON  CHRISTIAN HJORT  PER MÖLLER  JASON P. BRINER  ALA ALDAHAN  GÖRAN POSSNERT 《Boreas: An International Journal of Quaternary Research》2009,38(2):244-260

Previous work has presented contrasting views of the last glaciation on Jameson Land, central East Greenland, and still there is debate about whether the area was: (i) ice-free, (ii) covered with a local non-erosive ice cap(s), or (iii) overridden by the Greenland Ice Sheet during the Last Glacial Maximum (LGM). Here, we use cosmogenic exposure ages from erratics to reconcile these contrasting views. A total of 43 erratics resting on weathered sandstone and on sediment-covered surfaces were sampled from four areas on interior Jameson Land; they give ¹⁰Be ages between 10.9 and 269.1 kyr. Eight erratics on weathered sandstone and till-covered surfaces cluster around ∼70 kyr, whereas ¹⁰Be ages from erratics on glaciofluvial landforms are substantially younger and range between 10.9 and 47.2 kyr. Deflation is thought to be an important process on the sediment-covered surfaces and the youngest exposure ages are suggested to result from exhumation. The older (>70 kyr) samples have discordant ²⁶Al and ¹⁰Be data and are interpreted to have been deposited by the Greenland Ice Sheet several glacial cycles ago. The younger exposure ages (≤70 kyr) are interpreted to represent deposition by the ice sheet during the Late Saalian and by an advance from the local Liverpool Land ice cap in the Early Weichselian. The exposure ages younger than Saalian are explained by periods of shielding by non-erosive ice during the Weichselian glaciation. Our work supports previous studies in that the Saalian Ice Sheet advance was the last to deposit thick sediment sequences and western erratics on interior Jameson Land. However, instead of Jameson Land being ice-free throughout the Weichselian, we document that local ice with limited erosion potential covered and shielded large areas for substantial periods of the last glacial cycle.  相似文献