ZHU Yan, CHEN Fa hu, ZHANG Jia wu, AN Cheng bang. Effects of Depositional Environment on Pollen Assemblages—A case study in the Shiyang River Basin[J]. Acta Sedimentologica Sinica, 2001, 19(2): 186-191.
| Citation:
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ZHU Yan, CHEN Fa hu, ZHANG Jia wu, AN Cheng bang. Effects of Depositional Environment on Pollen Assemblages—A case study in the Shiyang River Basin[J]. Acta Sedimentologica Sinica, 2001, 19(2): 186-191.
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Effects of Depositional Environment on Pollen Assemblages—A case study in the Shiyang River Basin
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1 Northwest Normal University,Department of Geography,Lanzhou 730070;
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2 Lanzhou University,Resources and Environment School,Lanzhou 730000
- Received Date: 2000-04-27
- Rev Recd Date:
2000-06-22
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Abstract
The differences of the pollen assemblages of three sites in Shivang River basin, an internal river system in the arid area of Northwest China are so sharp that they can' t he explained by climatic change.The early to mid-Holocene pollen assemhlage of Sanjiaocheng section located at the end of Shivang River basin is dominated by the conifer. The surface samples of a site closed by the Sanjiaocheng Section has over 90% of xeromophte in the pollen assemblages.The pollen in the lower part of Hongshui River Secton is mainly xeric herb.In the upper part of the same section however conifer is dominant. Based on the analyses of sedimentary facies, depositional environments and the transportion characteristics of modern pollen we proposed that the obvious difference of pollen assemblages in the catchment are caused by the differences of depositional environments.As the Sanjiaocheng Section is near to the inlet of Shivang River to the paleo-lake with a semi-enclosed environmenu the sediments including pollen transported by water from the upper reaches would settle down there.The pollen assemhlage, therefore represents the vegetation of the upper reaches of the drainage.the Hongshui River Section is located near the end of the Hongshui River a tributary of Shivang River. The lower part of the section is alluvial sediments indicating an open flowing environment where only a small portion of the pollen carried by water can he kept in the sediments.There is no environmental significance in this pollen assemblage and it can' t he used to explain the vegetation.The upper part of the section is lacustrine sediments suggesting an enclosed environment similar to that in Sanjiaocheng Section.The pollen assemblage also reflects the vegetation in the uplands.The prevailing xeromophte in the surface sample near the Sanjiaocheng section implies the local desert vegetation because there is no water to the lowest reaches of the Shivang River as several reservoirs were built for irrigation in the upper and middle reaches.We have to he very careful when reconstructing or explaining palaeoenvironment with pollen assemblages only.Sedimentary fades and environment should also he given enough consideration as it is useful in judging the origin of pollen in the sediments.
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