The driving mechanism of the high-frequency lithofacies cycles in the Middle Jurassic Xiali Formation in the Yanshiping area, northern Xizang
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摘要: Walsh频谱分析引用不连续的方波代替傅里叶频谱分析中连续的正弦波和余弦波,由于Walsh函数的不连续性,它广泛应用于地层旋回周期的检测。藏北雁石坪地区中侏罗统夏里组发育一套以砂岩、泥岩为主的高频岩相旋回,在地层颜色上也表现出较好的旋回性。对该组地层岩性和颜色进行Walsh频谱分析对比发现,岩性频谱曲线及颜色频谱曲线的主频周期与米兰科维奇旋回周期之间均具有极好的对应关系,认为海平面的周期性变化是夏里组高频岩相旋回的驱动机制。同时根据岩性旋回频谱和颜色旋回频谱计算得出夏里组的沉积速率约为0.111m/ka,沉积持续时间约为3.689Ma。Abstract: The Walsh spectral analysis employs the discontinuous square waves or Walsh function instead of the continuous sine and cosine waves of the Fourier analysis. Because the Walsh function is discontinuous itself, the Walsh spectral analysis is widely used in detecting the periods in stratigraphic cycles. A succession of highfrequency lithofacies cycles composed of sandstone and mudstone occur in the Middle Jurassic Xiali Formation in the Yanshiping area, northern Xizang. According to the analysis of lithology and tinctures using the Walsh power spectra and filtering, the significant peak periods on both lithology and dinctorial spectra are in a very good correspondence with the Milankovtch cycles. The sea-level periodic changes are interpreted as the driving mechanism of the high-frequency lithofacies cycles in the Xiali Formation. The sedimentary duration of the whole Xiali Formation is about 3.689 Ma, with a sedimentary rate of about 0.111 m/ka.
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