Abstract:

Ten typical well cores were observed to study highfrequency sequence classification of Daqing Yaojia Formation in this paper. As a result, 98 ultrashortterm cycles, 33 shortterm cycles, 9 midterm cycles and 3 longterm cycles were identified. Meanwhile, this paper analyzed the Milankovitch Cycles, based on the natural gamma curves of those wells. The result showed that Milankovitch Cycles were well preserved in the strata of Yaojia Formation. The thickness of longperiod cycles caused by eccentricity ranges from 2.679 m to 3.972 m, the thickness of midperiod cycles caused by obliquity cycles ranges from 1.379 m to 2.131 m and the thickness of shortperiod cycles caused by precessions ranges from 0.601 m to 0.901 m. There is a good consistency between highfrequency sequences and Milankovitch Cycles. The midcycle, shortcycle and ultrashortterm cycles of highfrequency sequence are corresponding respectively to the longperiod eccentricity, shortperiod eccentricity and the precession cycle of Milankovitch Cycles. Lake level change caused by the change of Earths orbit is a major controlling factor of the formation of highfrequency sequences.

Key words: Daqing Placanticline, Yaojia Formation, high frequency sequence, Milankovitch Cycle, lake level change