Origin and Character of Loesslike Silt in the Southern Qinghai-Xizang (Tibet) Plateau, China
Origin and Character of Loesslike Silt in the Southern Qinghai-Xizang (Tibet) Plateau, China U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1549 Cover. View south-southeast across Lhasa He (Lhasa River) flood plain from roof of Potala Pal ace, Lhasa, Xizang Autonomous Region, China. The Potala (see frontispiece), characteristic sym bol of Tibet, nses 308 m above the valley floor on a bedrock hill and provides an excellent view of Mt. Guokalariju, 5,603 m elevation, and adjacent mountains 15 km to the southeast These mountains of flysch-like Triassic clastic and volcanic rocks and some Mesozoic granite character ize the southernmost part of Northern Xizang Structural Region (Gangdese-Nyainqentanglha Tec tonic Zone), which lies just north of the Yarlung Zangbo east-west tectonic suture 50 km to the south (see figs. 2, 3). Mountains are part of the Gangdese Island Arc at south margin of Lhasa continental block. Light-tan areas on flanks of mountains adjacent to almost vegetation-free flood plain are modern and ancient climbing sand dunes that exhibit evidence of strong winds. From flood plain of Lhasa He, and from flood plain of much larger Yarlung Zangbo to the south (see figs. 2, 3, 13), large dust storms and sand storms originate today and are common in capitol city of Lhasa. Blowing silt from larger braided flood plains in Pleistocene time was source of much loesslike silt described in this report. Photograph PK 23,763 by Troy L. P6w6, June 4, 1980. ORIGIN AND CHARACTER OF LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA Frontispiece.
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