Last glacial climate instability documented by coarse-grained sediments within the loess sequence, at Fanjiaping, Lanzhou, China

2009 ◽  
Vol 72 (1) ◽  
pp. 91-102 ◽  
Author(s):  
Hanchao Jiang ◽  
Ping Wang ◽  
Jessica Thompson ◽  
Zhongli Ding ◽  
Yanchou Lu
Keyword(s):  
Grain Size ◽  
Northern Hemisphere ◽  
Summer Monsoon ◽  
Luminescence Dating ◽  
Forest Recovery ◽  
Coarse Grained ◽  
Significant Information ◽  
Climatic Fluctuations ◽  
Last Glacial ◽  
Mis 3

AbstractOptically Stimulated Luminescence dating, grain-size analysis and magnetic susceptibility measurements were conducted on the Fanjiaping loess section, from the western Chinese Loess Plateau. The results confirm that last glacial high-frequency climatic shifts were documented in mid-latitude continental archives. The grain-size record indicated that coarse-grained sediments with horizontal bedding and channel-fill structures were only deposited in several short intervals, equivalent to the beginning of marine oxygen isotope stage (MIS) 4 and the early to middle MIS 3. This probably implies brief rainfall intensification of the Asian summer monsoon, and its disappearance since the late MIS 3 to MIS 2 may have been a response to significant glacial cooling in the Northern Hemisphere. Previous investigations revealed high sea-surface temperatures at high latitudes at the start of MIS 4, and the early to middle MIS 3 intensification of summer insolation in the Northern Hemisphere, implying evident climate amelioration. Climate improvement favors boreal forest recovery, enhancing both winter and summer air temperatures. The resultant smaller equator-polar temperature gradient probably helped the moisture-laden summer monsoon to penetrate northward. This study thus provides new significant information about the response of terrestrial loessic palaeoenvironments to millennial-timescale climatic fluctuations during the last glacial period.

Accretional soil formation in northern hemisphere loess regions - evidence from OSL-dating of the P/H climatic transition from China, Europe and North America

2021 ◽  
Author(s):  
Daniela Constantin ◽  
Joseph Mason ◽  
Ulrich Hambach ◽  
Daniel Veres ◽  
Cristian Panaiotu ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
High Resolution ◽  
Northern Hemisphere ◽  
Weighted Average ◽  
Luminescence Dating ◽  
Chinese Loess Plateau ◽  
The Holocene ◽  
Last Glacial ◽  
Climatic Transition ◽  
The Last Glacial

<p>Here we investigate the timing of Pleistocene-Holocene climatic transition as reflected in nine luminescence dated loess-palaeosol sequences across the northern hemisphere, from the Chinese Loess Plateau, the southeastern European loess belt and the central Great Plains, Nebraska, USA.<br>First, logs of high-resolution magnetic susceptibility and its frequency dependence were used as palaeoclimatic proxies to define the environmental transition from the last glacial loess to the current interglacial soil. Second, the onset of increase in their values above typical loess values was used to assess the onset of, and developments during, the Pleistocene-Holocene climatic transition. The variability seen in the magnetic susceptibility records are interpreted based on high-resolution luminescence dating applied on multiple grain-sizes (4-11 µm, 63-90 µm, 90-125 µm) of quartz extracts from the same sample. In order to increase the overall precision of the luminescence based chronology we rely on weighted average ages. Based on these, Bayesian modeling allowed the determination of age-depth models and mean sedimentation rates for each investigated site.<br>The magnetic susceptibility signal shows a smooth and gradual increase for the majority of the sites from the typical low loess values to the interglacial ones. At all but one site, this increase, associated to the onset of the Pleistocene-Holocene boundary (ie., 11.7 ka) was dated to 14 ka or even earlier. Our results highlight the need of combining palaeoclimatic proxies (magnetic susceptibility) with absolute dating when placing the Pleistocene-Holocene climatic transition as reflected by the evolution of this proxy in order to avoid misinterpretations in loess-paleosol records caused by simple pattern correlation. These results indicate diverse environmental dynamics recorded in the different North Hemisphere loess regions during the major global climatic shift from the last glacial to the Holocene.<br>The detailed luminescence chronology coupled with magnetic susceptibility records indicate the formation of accretional Holocene soils in the sites investigated. Modeled accumulation rates for the Holocene soil are similar for European, Chinese and American loess sites investigated and vary from 0.02 m/ka to 0.09 m/ka.</p>

scholarly journals A composite <sup>10</sup>Be, IR-50 and <sup>14</sup>C chronology of the pre-Last Glacial Maximum (LGM) full ice extent of the western Patagonian Ice Sheet on the Isla de Chiloé, south Chile (42° S)

2021 ◽  
Vol 70 (1) ◽  
pp. 105-128
Author(s):  
Juan-Luis García ◽  
Christopher Lüthgens ◽  
Rodrigo M. Vega ◽  
Ángel Rodés ◽  
Andrew S. Hein ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Luminescence Dating ◽  
Climate History ◽  
Ice Dynamics ◽  
Last Glacial ◽  
Mountain Glaciers ◽  
Mis 3 ◽  
Past Climate Change

Abstract. Unanswered questions about the glacier and climate history preceding the global Last Glacial Maximum (LGM) in the southern temperate latitudes remain. The Marine Isotope Stage (MIS) 3 is normally understood as a global interstadial period; nonetheless its climate was punctuated by conspicuous variability, and its signature has not been resolved beyond the polar realms. In this paper, we compile a 10Be depth profile, single grain infrared (IR) stimulated luminescence dating and 14C samples to derive a new glacier record for the principal outwash plain complex, deposited by the western Patagonian Ice Sheet (PIS) during the last glacial period (Llanquihue Glaciation) on the Isla de Chiloé, southern Chile (42∘ S). In this region, the Golfo de Corcovado Ice Lobe left a distinct geomorphic and stratigraphic imprint, suitable for reconstructing former ice dynamics and timing of past climate change. Our data indicate that maximum glaciation occurred by 57.8±4.7 ka without reaching the Pacific Ocean coast. Ice readavanced and buttressed against the eastern side of the Cordillera de la Costa again by 26.0±2.9 ka. Our data further support the notion of a large ice extent during parts of the MIS 3 in Patagonia and New Zealand but appear to contradict near contemporaneous interstadial evidence in the southern midlatitudes, including Chiloé. We propose that the PIS expanded to its full-glacial Llanquihue moraines, recording a rapid response of southern mountain glaciers to the millennial-scale climate stadials that punctuated the MIS 3 at the poles and elsewhere.

scholarly journals Submarine lava deltas of the 2018 eruption of Kīlauea volcano

2021 ◽  
Vol 83 (4) ◽  
Author(s):  
S. Adam Soule ◽  
Michael Zoeller ◽  
Carolyn Parcheta
Keyword(s):  
Grain Size ◽  
Pore Pressure ◽  
Mechanistic Model ◽  
Large Fraction ◽  
Volcanic Hazards ◽  
Lava Flows ◽  
Coarse Grained ◽  
Fine Grained ◽  
Fine Grain ◽  
Delta Formation

AbstractHawaiian and other ocean island lava flows that reach the coastline can deposit significant volumes of lava in submarine deltas. The catastrophic collapse of these deltas represents one of the most significant, but least predictable, volcanic hazards at ocean islands. The volume of lava deposited below sea level in delta-forming eruptions and the mechanisms of delta construction and destruction are rarely documented. Here, we report on bathymetric surveys and ROV observations following the Kīlauea 2018 eruption that, along with a comparison to the deltas formed at Pu‘u ‘Ō‘ō over the past decade, provide new insight into delta formation. Bathymetric differencing reveals that the 2018 deltas contain more than half of the total volume of lava erupted. In addition, we find that the 2018 deltas are comprised largely of coarse-grained volcanic breccias and intact lava flows, which contrast with those at Pu‘u ‘Ō‘ō that contain a large fraction of fine-grained hyaloclastite. We attribute this difference to less efficient fragmentation of the 2018 ‘a‘ā flows leading to fragmentation by collapse rather than hydrovolcanic explosion. We suggest a mechanistic model where the characteristic grain size influences the form and stability of the delta with fine grain size deltas (Pu‘u ‘Ō‘ō) experiencing larger landslides with greater run-out supported by increased pore pressure and with coarse grain size deltas (Kīlauea 2018) experiencing smaller landslides that quickly stop as the pore pressure rapidly dissipates. This difference, if validated for other lava deltas, would provide a means to assess potential delta stability in future eruptions.

scholarly journals Paleoenvironments from robust loess stratigraphy using high-resolution color and grain-size data of the last glacial Krems-Wachtberg record (NE Austria)

2020 ◽  
Vol 248 ◽  
pp. 106602
Author(s):  
Tobias Sprafke ◽  
Philipp Schulte ◽  
Simon Meyer-Heintze ◽  
Marc Händel ◽  
Thomas Einwögerer ◽  
...  
Keyword(s):  
Grain Size ◽  
High Resolution ◽  
Last Glacial ◽  
Size Data ◽  
The Last Glacial

The Effect of Grain Size on Superplastic Deformation of Ti-6Al-4V Alloy

2007 ◽  
Vol 551-552 ◽  
pp. 387-392 ◽  
Author(s):  
Wen Juan Zhao ◽  
Hua Ding ◽  
D. Song ◽  
F.R. Cao ◽  
Hong Liang Hou
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Superplastic Deformation ◽  
Initial Strain Rate ◽  
Deformation Mode ◽  
Tensile Tests ◽  
Optical Microscope ◽  
Coarse Grained ◽  
Transmission Electron ◽  
Grain Growth Model

In this study, superplastic tensile tests were carried out for Ti-6Al-4V alloy using different initial grain sizes (2.6 μm, 6.5μm and 16.2 μm) at a temperature of 920°C with an initial strain rate of 1×10-3 s-1. To get an insight into the effect of grain size on the superplastic deformation mechanisms, the microstructures of deformed alloy were investigated by using an optical microscope and transmission electron microscope (TEM). The results indicate that there is dramatic difference in the superplastic deformation mode of fine and coarse grained Ti-6Al-4V alloy. Meanwhile, grain growth induced by superplastic deformation has also been clearly observed during deformation process, and the grain growth model including the static and strain induced part during superplastic deformation was utilized to analyze the data of Ti-6Al-4V alloy.

Structure of Low Cobalt Alloy for Permanent Magnets of Basis System Fe-Cr-Co at Complex Two-Level Loading in Isothermal Conditions

2007 ◽  
Vol 539-543 ◽  
pp. 2928-2933 ◽  
Author(s):  
V.S. Yusupov ◽  
A.I. Milyaev ◽  
Galia F. Korznikova ◽  
Alexander V. Korznikov ◽  
J.K. Kovneristii
Keyword(s):  
Grain Size ◽  
Active Zone ◽  
Single Phase ◽  
Permanent Magnets ◽  
Phase Region ◽  
The Body ◽  
Coarse Grained ◽  
Isothermal Conditions ◽  
Basis System ◽  
Level Loading

Results of experimental research into evolution of the structure and microhardness of the hard magnetic Fe-30Cr-8Co-0,7Ti-0,5V-0,7Si alloy during complex two-level loading (compression + torsion) in isothermal conditions at various temperatures in single-phase region are reported. It was revealed that the deformation leads to a strong refinement of initial coarse-grained structure in the whole volume of the sample, however the generated structure is non-uniform through the body of the sample. In an active zone of deformation, near to mobile head, there is a microcrystalline layer with a grain size of about 5 microns which thickness poorly depends on the formation. With removal from the active zone of deformation the grain size increases, and microhardness decreases.

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