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我国西北甘肃群的新近纪沉积包含风成和水成类型的沉积物,研究这些沉积物的物质来源对于揭示中新世时期的干旱区分布及大气环流格局以及区域构造和地貌演化具有重要意义.通过碎屑锆石U-Pb年龄物源示踪方法,分别对该区发育于基岩台地与沉陷盆地的典型风成和水成沉积物进行了研究,并与周边的西秦岭和六盘山物质以及来源于亚洲内陆地区的第四纪黄土进行了对比.结果表明:(1)研究区中新世风尘堆积代表性样品的碎屑锆石年龄谱与西秦岭剥蚀物及天水中新世河流沉积样品显著不同,而与第四纪黄土-古土壤的锆石年龄谱十分相似,表明中新世风成堆积与第四纪黄土具有相似的物源区,进一步印证了前人提出的中新世时期的干旱区分布及大气环流的宏观格局与第四纪基本类似的观点;(2)天水地区11.5 Ma的河流相样品的锆石年龄谱明显不同于西秦岭剥蚀物,而与其东部的六盘山一致,指示着六盘山可能早在11.5 Ma以前就存在隆升剥蚀.
The Neogene sediments of the Gansu group in northwestern China contain aeolian and hydrothermal sediments. It is of great significance to reveal the source of these sediments for revealing the distribution of the arid region and the general circulation pattern and the regional tectonic and geomorphological evolution during the Miocene. Based on the U-Pb zircon dating from detrital zircons, the typical aeolian and sediment deposits developed in bedrock and subsidence basins in this area were studied respectively, and were compared with those of the surrounding West Qinling and Liupan Mountains And the Quaternary loess originating from the interior of Asia.The results show that: (1) The detrital zircon ages of the representative samples of the Miocene aeolian deposits in the study area are related to the erosion of the West Qinling and the Tianshui Miocene Sedimentary samples were significantly different from those of Quaternary loess-paleosol, indicating that the Miocene wind accumulation had similar provenance with Quaternary loess, further confirming the previous Miocene (2) The zircon ages of the 11.5 Ma river samples in the Tianshui area are obviously different from those in the West Qinling Mountains, and are similar to the Quaternary. Liupan consistent with its eastern, possibly as early as indicative of Liupan there uplift erosion in 11.5 Ma ago.