China
Africa
Explore chapters and articles related to this topic
Sediments and Sedimentary Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
We call rocks that have very thin layers—less than 1 centimeter thick— laminated. The sandstone shown in Figure 8.44 is a good example. Note that the layers in this photo are mostly, but not entirely, parallel. Ripples, created by the wind that deposited the sediment, disrupt the parallel layers. Some laminated sediments and rocks exhibit rhythmic layering—meaning that they contain alternating parallel layers that have distinctly different characteristics. Varves (see the example in Fig. 8.38) that form in meltwater lakes, for example, typically show rhythmic layering caused by seasonal changes in deposition.
Time Series Regression and EDA
Published in Robert H. Shumway, David S. Stoffer, Time Series: A Data Analysis Approach Using R, 2019
Robert H. Shumway, David S. Stoffer
Melting glaciers deposit yearly layers of sand and silt during the spring melting seasons, which can be reconstructed yearly over a period ranging from the time deglaciation began in New England (about 12,600 years ago) to the time it ended (about 6,000 years ago). Such sedimentary deposits, called varves, can be used as proxies for paleoclimatic parameters, such as temperature, because, in a warm year, more sand and silt are deposited from the receding glacier. The top of Figure 3.9 shows the thicknesses of the yearly varves collected from one location in Massachusetts for 634 years, beginning 11,834 years ago. For further information, see Shumway and Verosub (1992).
Sedimentary Environments and Facies
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
Morphological and sedimentological characters of large lakes and shallow ocean basins overlap in many respects. Rivers debouching into large lakes produce fan-shaped deltas similar to those bordering seas. In cross-section these show simple, steep foresets overlain by flat topsets (typical Gilbert-type delta). The finer sediments deposited at the lake centre below an active wave base are generally thin bedded and parallel laminated. Varves may develop as seasonal deposits within lakes located in a temperate climate. Storm surges produce hummocky cross-stratifications that are smaller in dimensions than those formed under marine conditions.
LiDAR-based mapping of paleo-ice streams in the eastern Great Lakes sector of the Laurentide Ice Sheet and a model for the evolution of drumlins and MSGLs
Published in GFF, 2018
Shane Sookhan, Nick Eyles, Niko Putkinen
Younger later Wisconsinan glacial events are much better constrained and there is widespread agreement that at c. 14,500 ybp the margin of the Ontario-Erie lobe lay against the Lake Escarpment Moraine in western New York, the Ashtabula Moraine in western Pennsylvania and the Defiance/Lavery moraine system in northern Ohio (Horton 2015); an event classically known as the Port Bruce Stade (Karrow et al. 2000; Kozlowski et al. 2018). At this time, the Ontario-Erie lobe reached just beyond the southern ends of the Finger Lakes to deposit the glaciofluvial VHM sometime between ~14.8 and 13.6 ka (Krall 1977; Muller & Calkin 1993; Ridge 2003, 2004; Ridge et al. 1991, 2012) and “most likely ~14.4 ka” (Mullins et al. 1996, p. 31). Correlation of VHM and related moraines across New York State varies from one worker to another but all are agreed with the classical mapping of Goldthwait (1922) in showing ice flowing down the topographic depression occupied by Oneida Lake to abut ice flowing in the other direction up the Mohawk Valley from the Hudson Valley (Krall 1977; Muller & Calkin 1993; Millar 2004; Ellis et al. 2004; Kappel et al. 2007; Ridge et al. 2012; Kozlowski et al. 2018, Fig. 1). VHM has been correlated with moraines in Pennsylvania and Ohio, where it marks the furthest westward extent of the Ontario-Erie Lobe at c. 14,500 ybp and records the last time ice advanced into Ohio (Szabo & Bruno 1997). Possible VHM equivalents have been correlated to still-stand positions in the Hudson Valley at 14,600 and 14,500 ybp using the North American Varve Chronology (see Figs. 6 and 7 in Ridge 2004; Ridge et al. 2012).
Dynamics of a retreating ice sheet: a LiDAR study in Värmland, SW Sweden
Published in GFF, 2020
Alastair Goodship, Helena Alexanderson
Historically, the study of ice sheet dynamics has been based upon observations of existing ice sheets and glaciated areas and upon studies of landforms and glacial deposits in previously glaciated regions such as northern Europe and North America. In both cases reliable, consistent observations stretch back ~200 years and have relied on physical investigation and geological mapping of features often complemented by study of aerial photography and satellite imagery in later years. The Swedish varve chronology and the techniques developed to constrain it have been key tools in determining ice-sheet retreat rates in the area beneath the Scandinavian Ice Sheet (SIS) and also in other formerly glaciated regions (Zillén et al. 2003; DeJong et al. 2013; Stroeven et al. 2016; Brooks 2018). In many regions, the glacial landforms that are key to determining past ice-sheet behaviour are often masked or obscured by forest, later Quaternary deposits or by anthropological activities and features. Advances in remote sensing and observations within the last 20 years have produced a powerful new set of resources for the study of previously glaciated areas. Of particular importance is the advent of Light Detection and Ranging (LiDAR) surveying (Dowling et al. 2013) and the production of high resolution detailed land surface maps (Digital Elevation Models, DEMs). These maps are now key resources for the study of glacial features and geomorphology and have seen increasing use in recent years. A prominent example of this technique in use is the Swedish National height model, which has used LiDAR to reveal the glacial landscape of Sweden in detail never seen before (Johnson et al. 2015). It is now possible to define a greater range and higher concentration of relict glacial landforms. This allows detailed investigation of the dynamics of the retreating SIS.
The Holocene of Sweden – a review
Published in GFF, 2022
More than 125 years of research have produced a wealth of information on Holocene climate variability in Sweden. The main features of Holocene climate variation were already known in the early part of the 1900s, but later investigations have provided more detailed information on the timing and magnitude of climate events. The Blytt–Sernander scheme, originally developed in the early 1900s by Sernander (1908), building on Blytt's studies of Danish peat bogs (Blytt 1876), is still in use but should be avoided in favour of the new formalised tripartite subdivision of the Holocene (Walker et al. 2019). The last decades have seen development of many new proxies and methods as well as new applications of traditional methods. Multi-proxy analyses are becoming increasingly common in palaeoclimatology and many recent examples from Sweden show that strengths and weaknesses in palaeoclimate reconstructions can be identified and assessed. The present review, however, shows that several research questions remain unresolved and need to be addressed in the future: Was the early Holocene climate warming synchronous over Sweden (and with NW Europe)?Is there evidence in Sweden for other early Holocene events than the PBO/11.4 and 8.2 ka BP events?How reliable is the varve-based deglaciation chronology for Sweden (and where are the “missing varves”)?When and where did the last remnants of the Scandinavian ice-sheet melt?What characterises the 8.2 ka BP event in Sweden?When did Swedish glaciers start to reform in the Middle Holocene (or earlier?)Why was the HTM in southern Sweden delayed in relation to the summer insolation maximum?When did the HTM come to an end in Sweden, c. 5500 or 4200 cal a BP?Was the 4.2 ka BP event significant in Sweden?Is there a link between Holocene climate events and human population bottlenecks in Fennoscandia?Which late-Holocene event was most prominent and had the strongest effect on human societies in Sweden?When did permafrost inception in northern peatlands start in the Late Holocene, before LIA or at the inception of LIA?