ADVANCE OF GEOCHRONOLOGICAL DATING OF SHEXING FORMATION IN THE LHUNZHUB BASIN, LHASA AREA AND ITS SIGNIFICANCE
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Abstract:
New materials of sporopollen from the upper part of Shexing Formation of the Dzhong-Nama section in the Lhunzhub Basin of Lhasa block are reported in this paper. Characteristics of the sporopollen assemblage are:Most of the found sporopollen are common elements of Paleogene, so the related strata are impossible to be Cretaceous sediments; The assumed deciduous and latifoliate vegetation including Alnipollenites, Betulaepollenites, Carpiniptes, Quercoidites, Juglanspollenites, Ulmipollenites, Tiliaepollenites et al., are dominant in this assemblage. It indicates that the climate was not droughty when they deposited; Triporopollenites and Tricolporopllenites which are dominant in Early Paleogene, occurred in little amount in the present assemblage. The sporopollen assemblage is closer to those of the middle and late Paleogene, and its age may be Late Eocene. The Shexing Formation contains not only the upper part of the Upper Cretaceous, but also part of Paleogene. The latest age of the Shexing Formation may be Late Eocene. Based on the aboved conclusion, the unconformity between the Shexing Formation and Linzizong Group may represent the post-Eocene tectonic movement. The unconformity does not represent tectonic movement at the Cretaceous- Paleogene boundary. At the same time, Paleogene fluvial-lacustrine strata might have been deposited in the Lhunzhub Basin.
