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Major-element and stable-isotope geochemistry of fluid inclusions in halite, Qaidam Basin, western China: Implications for late Pleistocene/Holocene brine evolution and paleoclimates

By
Tim K. Lowenstein
Tim K. Lowenstein
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Ronald J. Spencer
Ronald J. Spencer
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Yang Wenbo
Yang Wenbo
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Enrique Casas
Enrique Casas
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Zhang Pengxi
Zhang Pengxi
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Zhang Baozhen
Zhang Baozhen
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Fan Haibo
Fan Haibo
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H. Roy Krouse
H. Roy Krouse
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Published:
January 01, 1994

Salt cores from the nonmarine Qaidam Basin, western China, are used to interpret late Pleistocene/Holocene paleoclimate and brine evolution based on major elements and stable isotopes (hydrogen and oxygen) in fluid inclusions in halite. Layered primary halite with chevron and cumulate textures diagnostic of crystallization at the brine bottom and at the air-brine interface occurs to depths of 43 m (54 kyr B.P. based on U-series dating methods). Fluid inclusions in this halite contain the lake brines from which the halite crystallized. Variations in the major-element chemistry and activity of H2O in fluid inclusions with depth/time reflect changes in the ratio of inflow to evaporation and document relative basin aridity. Stable isotopes of hydrogen and oxygen in fluid inclusion waters are used to interpret paleoclimate in terms of surface temperatures, although atmospheric circulation patterns, sources of moisture, and other factors may also influence isotopic compositions. Relative CO2/N2 in fluid inclusions from cumulate halite that contain trapped air preserve a record of atmospheric chemistry.

Fluid inclusions in halite crystals 20 to 13 kyr B.P. in age have exceptionally low δ18O, δD, and C02, which coincides with the marine oxygen isotope record and the polar ice core record of global cooling during the last glacial period. At this time, halite precipitated from concentrated saline lake brines in the cool, but hyperarid, Qaidam Basin. Fluid inclusions in salt cores suggest that regional aridity may have limited glaciation on the Qinghai-Tibet Plateau during the last glacial, compared to North America and other areas.

Fluid inclusions in halite from 13 kyr B.P. to the present in age have increased δ18O, δD, salinity CO2, indicating probable warming during the glacial-interglacial transition and the Holocene; warm, arid conditions have persisted to the present. The modern Qaidam Basin, which contains the world’s largest modern deposits of potash evaporites, represents the driest climate of the 50-kyr-B.P. record.

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Contents

GSA Special Papers

Paleoclimate and Basin Evolution of Playa Systems

Michael R. Rosen
Michael R. Rosen
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Geological Society of America
Volume
289
ISBN print:
9780813722894
Publication date:
January 01, 1994

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