China
Africa
Explore chapters and articles related to this topic
Atmospheric Effects
Published in Wayne T. Davis, Joshua S. Fu, Thad Godish, Air Quality, 2021
Wayne T. Davis, Joshua S. Fu, Thad Godish
Glacial periods lasting thousands of years were characterized by the development and movement of massive ice sheets (several kilometers thick) over parts of the northern hemisphere. They were followed by climatic warming and glacial retreat. The last large glacier over North America receded approximately 12,000 years ago. The Earth is presently in an interglacial warming period.
Origin, Usage and Production of Unbound Granular Materials for Road Construction
Published in A. Gomes Correia, Fernando E.F. Branco, Bearing Capacity of Roads, Railways and Airfields, 2020
G. Bjarnason, H.G. Johansson, S. Davitt
During the last Ice age the massive, thick icecap in the northern hemisphere isostatically depressed the crust of the earth. Several thousand years after deglaciation, the land surface still continues to rise at an exponentially decreasing rate, and will continue to do so until the adjustment of isostacy is completed. The large volume of water, which was held by the vast inland ice sheet during the glacial period, was released after the ice age causing eustatic changes in the sea level. This effect, caused the sea level to rise above and cover what were previously land areas.
Deep foundations and the need for research on screw piles in Belgium.
Published in Jan Maertens, Noël Huybrechts, Belgian Screw Pile Technology Design and Recent Developments, 2020
In the northern part, the stratigraphy has been governed by fluctuations in the coastal line. Consequently, the bedrock is covered by alternating layers. Tertiary clay, sand and local gravel sediment are present, with overall thickness up to a hundred metres. The quaternary pleistocene formation has been greatly influenced by the glacial periods, giving rise to the formation of marine, coastal, river, lake or wind deposits of sand, clay, peat and silts or loess. Holocene erosion and river sedimentation, as well as human activities, have also influenced the current surface.
Geological setting of exceptional geological features of the Flinders Ranges
Published in Australian Journal of Earth Sciences, 2020
Neoproterozoic glaciogenic deposits are widely distributed on all continents except Antarctica but their distribution and mode of occurrence contrast with Phanerozoic analogues (Hoffman & Schrag, 2002). They provide evidence of the most widespread and long-ranging glaciations on Earth. Distinctive ‘cap’ carbonate layers sharply overlie most Neoproterozoic glaciogenic successions without significant hiatus, implying a sudden switch back to a warmer climate. However, in the Adelaide Geosyncline, a significant break, in places with erosion and even tectonic tilting, separates the Sturtian cap carbonate from the underlying glaciogenic sediments. Cap carbonates have unusual sedimentological, geochemical and isotopic characteristics not found in other Neoproterozoic or Phanerozoic carbonates and they occur even in successions otherwise lacking carbonate (Hoffman & Schrag, 2002). At least two major worldwide glacial periods are evident, interspersed with periods of relatively warm climate, with glaciers interpreted to reach sea-level at low paleolatitudes.
The geological process for gas hydrate formation in the Qilian Mountain permafrost
Published in Petroleum Science and Technology, 2019
Zhengquan Lu, Gangyi Zhai, Yinhui Zuo, Quanfeng Wang, Dongwen Fan, Shiqi Tang, Daodong Hu, Hui Liu, Ting Wang, Youhai Zhu, Rui Xiao
The uplift of the Qinghai-Tibet Plateau and the process of glaciations or permafrost formation are correlated. According to the research (Qi et al. 2014), the glacial drifts and the glacial alluvium deposits were found around the lake of Qinghai. These glacial drifts and the glacial alluvium deposits were formed during the last third glacial period or the maximal glacial period at the age of 0.5–0.7 Ma, the last second glacial period at the age of 130–300 Ka and the last glacial period at the age of 10–70 Ka, respectively. An evolutionary sequence was then preliminarily established during the quaternary glacial period and interglacial period in the region of the Qilian Mountain. Additionally, the palaeo-temperature and the palaeo-environment was also rebuilt during the quaternary glacial period and interglacial period in the region of the Qilian Mountain. Results showed that the permafrost formed in the region of the Qilian Mountain no later than the early Middle Pleistocene. Hence it is indirectly inferred that the gas hydrate formation time should be no later than the early Mid-Pleistocene in the Qilian Mountain.
Geology of New Zealand’s Sub-Antarctic Islands
Published in New Zealand Journal of Geology and Geophysics, 2019
James M. Scott, Ian M. Turnbull
Present-day geomorphology suggests that the Auckland Islands/Motu Maha underwent several periods of glacial erosion throughout the Pleistocene (e.g. Speight and Finlayson 1909; Turnbull 2006). Based on geomorphology, sea levels during glacial periods were as much as 150 m below present and the terraced surface of the Auckland Islands/Motu Maha shelf reflects this (Summerhayes 1967; Tidey and Hulbe 2018). At the glacial maximum, the Auckland Island group would have been a single large island with an ice cap (or caps) and glaciers possibly extending to the shelf edge (Turnbull 2006). Rainsley et al. (2018) name this event the Enderby Glaciation and date it at ca. 385 ka. During interglacial high sea level stands, the glacial valleys were presumably largely drowned, although little evidence of this remains except around Port Ross where Fleming et al. (1976) infer a raised marine erosion surface; the topographic influence of flat-lying lava flows makes recognition of wave-cut marine benches and cliffs difficult. The Matheson Bay sedimentary sequence may be related to a younger glacial period at c. 40–50 ka BP, although over-deepening of fjords and formation of moraine barriers (Tidey and Hulbe 2018) may have taken place slightly earlier, at ∼68 ka (Rainsley et al. 2018). The youngest cirque glaciers are still undated but were gone by ca. 15,000 yrs BP, which is the age of the oldest deposits within them (Rainsley et al. 2018). Cores extracted from Holocene sediments in onshore lakes and offshore fjords at Hanfield and Norman inlets record rapidly changing climate conditions and inferred strengthening of the westerly wind system (Browne et al. 2017).