| Qiangtang Basin is located in the north of the Tibetan Plateau and in the south of Qinghai, whose tectonic structures lie in the eastern section of the giant Tethys-Himalayan tectonic region, and is clamped among the Gangdise&Nyainqentanglha and Hoh Xil&Bayan Har..It will become the most promising oil detection area of marine basins in the Tibetan Plateau. Since Qiangtang marine basin is in the eastern section of the Neo-Tethys Ocean, which is paralleled with Central Asia Kalakum Jurassic period giant potash basin in the north of Tethys sea, both are basically with the same tectonic setting. But the degree of research of Qiangtang Basin is relatively low, it is urgent to make a further study of whether it is similar to the formations of potash deposits and position in Karakum Basin. Based on the study of predecessors’and first-hand research data of the profile, mainly through the analysis of Qiangtang Basin Yanshiping profile Xiali formations sratigraphy, lithology, sedimentary facies and description of the Xializu meter-scale sedimentary cycles characteristics, as well as the formation mechanism and results of the climate analysis study,, the author draws the conclusions as follows:1. Through the study and analysis of Xiali formations stratigraphy, characteristics of sedimentary petrology, and characteristics of paleontology, and combined with the profile data and study results of predecessors, the author believes that Xiali formations all are the tidal flat environment. Based on the features of stratigraphic sequence to carry on divide of tidal flat environment for the Xiali formations, the subphases separately are:supralittoral zone subphase, intertidal subphase (low tide flat, middle tidal flat, high tide mud flat) and subtidal zone subphase.2. The Yan shiping region Xiali formations (its thickness is about640m) formed152meter-scale cycles, which can be divided into clastic rock type and clastic-carbonatite rock type. The clastic rock type combination of them totally are12types, and the clastic-carbonatite rock type is also divided into six types, the common features they both have are that particles upward gradually tapering, depositional environment overall upward become deeper, with the character of tides "normal graded bed sequence".3. Through the climate change analysis of the CaCO3and SO42-, it reasons out that the climate has changed gradually from the semi-arid to arid environment. During the Middle Jurassic Xiali formations period, gradually arid changing events did occur.4. Through the spectrum analysis of spectrogram of the CaCO3, we know that the frequency of the diagram includes0.0081,0.027,0.063, and0.214which is corresponding to the wavelength of123,37.04,16.13,4.76(1:0.301:0.129:0.039) and the ratio is equal to or similar to the ratio among of eccentricity cycles400ka andl23ka, tilt ratio cycles50.6ka, and the precession cycle17.6ka (1:0.308:0.127:0.044), which indicates that the ratio among them has a good corresponding relationship between the ratio of the Milankovitch cycle ratio, It demonstates that it is the Milankovitch cycles that control the development of climate change.The above study reveals the importance of Xiali formations in the Qiangtang Basin, which will provide important basic information to the find and research and development of potash resources of Qiangtang Basin in the Jurassic period stratum. |
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