Search

This paper examines the distribution, stratigraphy and chronology of landslide deposits within the Gouffre Valley to provide a long-term context for the 1663 CE M 7.0–7.5 Charlevoix earthquake, Charlevoix-Kamouraska Seismic Zone (CKSZ), southern Quebec, Canada. Our mapping utilized a 1 × 1 m digital terrain model, and we interpreted deposit age and stratigraphy from 30 new AMS radiocarbon ages, supplemented by 51 regular radiocarbon ages and 23 dendrochronology ages compiled from previous studies. These data provide a robust chronological connection between the 1663 CE earthquake and large-scale landslide deposits that cover about 24 km2, extend about 20 km along the valley bottom, and originated from separate source areas. Eight, relatively small-scale (less than 0.48 km2), prehistoric landslide features are also present in the Gouffre Valley, including three dated landslides, aged between about 7950–7300, 6595–6087, and 1310–1200 cal BCE, a poorly-constrained deposit aged between 4782–4452 BCE and 1663 CE, and four landslides of unknown age. There is no evidence to support an earthquake trigger for any of these prehistoric landslides. Instead, the widespread deposits associated with the 1663 CE earthquake represent the only multi-event, landslide signature in the Gouffre Valley. This, in combination with a long gap between early postglacial and late Holocene mass movement activity in several nearby lakes, is consistent with the 1663 CE earthquake being the largest to occur in the CKSZ over the past about 10 ka. • Large-scale landslide deposits present along lower 20 km of Gouffre Valley. • Robust connection between age of landslides and strong 1663 CE earthquake. • No clusters of older, pre-1663, similarly-aged landslides in valley. • 1663 CE earthquake is largest to occur in CKSZ over the past roughly 10 ka. [ABSTRACT FROM AUTHOR]

This paper presents the results of a detailed microstructural study of a thick till formed beneath the Weichselian (Devensian) Odra palaeo-ice stream, west of Środa Wielkopolska, Poland. This SE-flowing ice stream was one of a number of corridors of faster flowing ice which drained the Scandinavian Ice Sheet in the Baltic region. Macroscopically, the massive, laterally extensive till which formed the bed of this ice stream lacks any obvious evidence of glaciotectonism (thrusting, folding). However, microscale analysis reveals that bed deformation was dominated by foliation development, recording progressive ductile shearing within a subhorizontal subglacial shear zone. Five successive generations of clast microfabric (S1 to S5) have been identified defining a set of up-ice and down-ice dipping Riedel shears, as well as a subhorizontal shear foliation coplanar to the ice-bed interface. Cross-cutting relationships between the shear fabrics record temporal changes in the style of deformation during this progressive shear event. Kinematic indicators (S-C and ECC-type fabrics) within the till indicate a consistent SE-directed shear sense, in agreement with the regional ice flow pattern. A model of bed deformation involving incremental progressive simple shear during till accretion is proposed. The relative age of this deformation was diachronous becoming progressively younger upwards, compatible with subglacial shearing having accompanied till accretion at the top of the deforming bed. Variation in the relative intensity of the microfabrics records changes in the magnitude of the cumulative strain imposed on the till and the degree of coupling between the ice and underlying bed during fast ice flow. [ABSTRACT FROM AUTHOR]

Since G. K. Gilbert's foundational work in the eastern Great Basin during the late 1800s, the late Pleistocene Lake Bonneville (30–10 ka) has been recognized as a natural laboratory for various Quaternary studies, including lithospheric deformation due to surface loading and climate-forced water balance changes. Such studies rely on knowledge of the elevations of Lake Bonneville's paleoshoreline features and depositional landforms, which record a complex history of lake level variations induced by deglacial climate change. In this paper, we present (1) a new compilation of 178 elevation measurements of shoreline features marking Lake Bonneville's greatest areal extent measured using high-precision differential GPS (dGPS), and (2) a reconstructed outline of the highest shoreline based on dGPS measurements, submeter-resolution aerial imagery, topographic digital elevation models (DEMs), and field observations. We also (3) devise a simplified classification scheme and method for standardizing shoreline elevation measurement for different shoreline morphologies that includes constraints on the position of the still water level (SWL) relative to each feature type. The deformation pattern described by these shoreline features can help resolve the relative effects of local hydro-isostasy due to the lake load and regional solid earth deflection due to the Laurentide ice sheet, with potential implications for Earth rheology, glacial isostatic adjustment, and eustatic sea level change. [ABSTRACT FROM AUTHOR]

In this paper we present a suite of erosional remnants, mega deposits and subtle bar morphology that we relate to the outburst flood from the glacial lake Nedre Glomsjø at the end of the last Ice Age. By using large datasets of airborne LiDAR data implemented in a geographic information system (GIS), we have mapped flood related features along the Glomma and Vrangselva rivers in southeastern Norway. The unprecedented overview of the valley reaches obtained by the vegetation-free LiDAR-derived digital elevation models (DEM) has revealed a set of hitherto undocumented landforms. Persisting erosive lines – indicators of the uppermost flooded level – are carved into surficial deposits in the hillsides and are found as high as 80–90 m above the modern valley floor. By using the indicators as an upper flood boundary, we have computed cross-sectional profiles showing that the flood in some reaches inundated more than 120 000 m 2 of the valley. Large, streamlined bed forms, which we interpret as flood bars, drape sections of the valley floor, some several kilometers long. The most morphologically striking – pendant bars – are developed behind flood flow projections, such as bedrock knolls or in lee of a valley bend. Flood bars occur in the entire study area, but are more widespread in the north and generally decrease in size moving in a downstream direction. Kettle holes and ice-block obstacle marks from icebergs arrested during the flood are common. These features support the theory of a catastrophic drainage event, but also indicate a pattern of differential erosion and deposition that allowed us to interpret palaeoflow on individual bars. Vast aeolian dune fields in the region are interpreted as a secondary product of the flood, as deposits related to the event were mobilised by northerly winds momentarily after the flood waned. The dune fields cover an excess of 50 km 2 and reveal that the region was a highly active periglacial desert after the flood. Our mapping highlights the outburst flood's role as a landscape-defining event. Morphological evidence determine the southern fringe of the Scandinavian ice sheet to c. 15 km north of Elverum at the time of the outburst flood. From calibrating existing 14 C dates we postulate an age of c. 10–10.4 cal ka BP for the Nedre Glomsjø drainage event and the contemporaneous margin of the ice sheet. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews our current understanding of Quaternary climate and landscape changes in the desert areas of northern China, a key portion of the middle-latitude drylands on Earth. Combining earlier studies with our recent research and experience, we offer a comprehensive picture of the state of Chinese deserts during the Quaternary and, in the interest of enhancing future research, identify knowledge gaps and areas of uncertainty. Lacustrine deposits found over an area ranging from China’s western Taklamakan Desert to the eastern Hunshandake Sandy Lands suggest that extensive lakes occurred in China’s deserts during the Pleistocene. Analysis of digital elevation models from SRTM (Shuttle Radar Topography Mission) data supports this interpretation and shows the significant extent of these former lakes. New estimates of mean annual evaporation of ca. 1000 mm from lake surfaces and ca. 100 mm from land surfaces, confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone, especially during intervals when the mean annual rainfall is more than 100 mm. Rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of China are very sensitive ephemeral systems, and not long-lasting as previously thought. Available chronologies suggest that there were large lakes in the western Taklamakan Desert and the Chadamu Basin during MIS (Marine Isotope Stage) 3, at ∼30 ka, probably related to a period of strong influence of northern hemispheric westerly winds. Channels and elevation models revealed by SRTM data and remains of lacustrine sediments also indicate that there was a large lake in the Hunshandake Sandy Lands in the eastern portion of the desert belt during the Quaternary. There is significant evidence that during the middle Holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern China. Lacustrine records from the Badain Jaran Desert in western Inner Mongolia suggest that it was generally dry before 10 cal ka, becoming wetter from 10 to 4 cal ka, and dry again afterwards. Study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt, suggests that there was a period of wet and warm climate in this region during the mid-Holocene Optimum, at a minimum between 6 ka and 4 ka, but possibly lasting longer. Recent observations dealing with the generation and transport of dust from Central Asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed. These results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in Chinese deserts are somehow similar to that having occurred in the Sahara Desert of North Africa. Deserts in northern China were also important focal regions for Neolithic cultures during intervals when environmental conditions supported a denser vegetative cover. There is evidence that some areas of woody vegetation to the west of Badain Jaran Desert were deforested by humans by ca. 4000 yr B P, although it is still debatable whether humans have had a significant impact in other areas at that time. Opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long-term, field-based, investigations. [Copyright &y& Elsevier]

The extent of proglacial lakes following the initial separation of the southwest Laurentide Ice Sheet from the Cordilleran Ice Sheet and its eastward retreat from the Canadian Rocky Mountains has been reconstructed across regions of Alberta at a range of scales. However, to date, no studies have integrated all available geological information to produce a province-wide deglacial reconstruction that considers the evolution of proglacial lakes as components of the ice-marginal system. In this paper, we utilize a geologically constrained shoreline projection method with a high resolution digital elevation model to reconstruct the evolution of the ice-marginal system along the southwest LIS during the last deglaciation. This method provides new details on the configuration, volume, drainage history and routing of ∼240 proglacial lakes as they migrated across Alberta and establishes a succession of paleogeographic reconstructions that can place geological evidence of regional and local ice-flow reorganizations into a spatiotemporal context. These reconstructions demonstrate that although the evolution of proglacial lakes was largely driven by the topography of the emerging landscape and the configuration of the ice margin, positive feedbacks in the ice-marginal system, particularly where margins transitioned from terrestrial to subaqueous settings played a major role in deglacial ice dynamics. Narrow, ribbon-shaped lakes that paralleled the ice margin induced relatively minor changes in style and rate of deglaciation, whereas the evolution of progressively larger, longer-lived lakes extending obliquely to the ice margin promoted surging and subsequent rapid retreat. • The retreating Laurentide Ice sheet dammed proglacial lakes over much of the Alberta area. • By using an outlet projection method we reconstruct proglacial lakes over the region. • We reconstruct the pattern of deglaciation from the relative sequence of proglacial lakes. • In the south relatively small proglacial lakes drained through spillways that formed along the lobate ice sheet margin. • In the north, larger proglacial lakes developed, promoting surging and subsequently rapid retreat of the ice sheet. [ABSTRACT FROM AUTHOR]