East Asian loess sequences

East Asian loess sequences
Name	East Asian loess sequences
Type	Sedimentary deposit
Period	Quaternary
Primary lithology	Loess, paleosol
Namedfor	Loess Plateau
Region	East Asia

East Asian loess sequences East Asian loess sequences are thick, windblown silty deposits that mantle parts of the Chinese Loess Plateau, the Loess Plateau margins, and adjacent basins in China, Mongolia, the Russian Far East, and the Korean Peninsula. These sequences provide high-resolution terrestrial archives linking orbital forcing, ice-sheet dynamics, and monsoon variability through the Quaternary and have informed debates involving the International Geophysical Year, the Bureau of Land Management (as land-management comparator studies), and major paleoclimate syntheses such as the Intergovernmental Panel on Climate Change assessments.

Definition and Geological Setting

East Asian loess sequences are defined as accumulations of aeolian silt and related paleosols distributed across the Chinese Loess Plateau, the Shaanxi-Gansu corridor, the Ordos Basin, and the Tarim Basin margins. They occur in settings influenced by the Asian monsoon system, proximity to the Gobi Desert, and pathways tied to the Westerlies and the East Asian winter monsoon. Important geographic anchors include the Yellow River, the Wei River, the Upper Yangtze, and the Mongolian Plateau, and these deposits often overlie bedrock units like the Loess Plateau basalts and Quaternary alluvium associated with regions such as Sichuan and Ningxia.

Stratigraphy and Sedimentology

Stratigraphically, sequences show alternating loess layers (L) and paleosols (S) that have been correlated with marine isotope stages recorded in cores from the North Atlantic, Iberian Margin, and the Ocean Drilling Program datasets. Key loess sections include the classic type-locality in Lingtai, and additional reference sections at Xifeng, Luochuan, and Baoji. Sedimentological characteristics—grain-size distributions, magnetic susceptibility contrasts, and carbonate concretions—are compared with lacustrine deposits from Lake Baikal, speleothem records from Shennongjia, and marine records from the East China Sea to interpret aeolian transport processes.

Chronology and Dating Methods

Chronologies for sequences integrate optically stimulated luminescence (OSL) dating from laboratories collaborating with institutions like the Chinese Academy of Sciences and the University of Oxford, radiocarbon dating of intercalated organic horizons where present, and paleomagnetic stratigraphy anchored to the Brunhes–Matuyama reversal. Tephrochronology links volcanic markers to eruptions recorded at Mount Changbai, Mount Fuji, and Tengchong units, while cosmogenic nuclide studies referencing the International Commission on Stratigraphy frameworks assist age models calibrated against the Astronomical Theory of Paleoclimates and Milankovitch cycles.

Paleoclimate and Paleoenvironmental Records

Loess sequences archive proxies—magnetic susceptibility, grain-size, geochemical tracers, and biomarker assemblages—that have been correlated with Greenland ice core records, the Vostok and EPICA cores, and the Mauretanian marine isotope stratigraphy. Interpretations tie stronger loess accumulation to enhanced East Asian winter monsoon circulation synchronous with ice-sheet expansion documented in the Laurentide Ice Sheet reconstructions and with stadial events recorded in the Younger Dryas and Heinrich events. Paleobotanical indicators in paleosols, compared with records from the Peking Man Site and cave sequences such as Shuidonggou, inform vegetation shifts between steppe, loess-steppe, and forest-steppe ecotones.

Regional Variability and Key Sequences

Major sequences exhibiting regional variability include the classic profiles at Luochuan, Lantian, Xifeng, and Lingtai on the Loess Plateau, peripheral sections in Inner Mongolia such as Mallin, and distal deposits in Northeast China. Comparative studies reference correlative records from Lake Huguang Maar and the Bohai Sea to resolve discrepancies in depositional rates attributed to factors like source proximity to the Gobi Desert, local tectonics along the North China Craton margin, and anthropogenic alteration beginning in the Neolithic and intensifying during the Ming Dynasty and Qing Dynasty.

Formation Processes and Sources

Formation is driven by entrainment from deflationary sources including the Gobi Desert, Badain Jaran Desert, and alluvial fans of the Yellow River and Liao River, with transport modulated by seasonal pressure systems such as the Siberian High and the Pacific Decadal Oscillation. Mineralogical fingerprints link loess composition to provenance regions like the Altai Mountains, the Tian Shan, and the Qinling range, while granulometric sorting reflects aeolian regimes described in studies associated with the American Geophysical Union and sediment transport theory developed in the Royal Society literature.

Human Interaction and Archaeological Significance

Loess landscapes host rich archaeological sequences including Paleolithic sites like Zhoukoudian, Shuidonggou, and Xiaochangliang, and Neolithic settlements such as Banpo and Yangshao culture localities. Loess preservation has influenced site formation processes evaluated by teams from the Chinese Academy of Social Sciences and international collaborations with the Smithsonian Institution and University of Tokyo, affecting interpretations of hominin occupation patterns linked to climatic episodes recorded in the sequences and to cultural responses during the Holocene Climatic Optimum and historic droughts documented in imperial archives like the Twenty-Four Histories.

Category:Geology of East Asia