Abstract:

The sedimentary facies of the Upper Jurassic Houcheng Formation silicified wood outcrops in north of Yanqing area are interpreted jointly with sedimentary structure and characters of sedimentary sequence.This area mainly developed braided river deposits. The main sedimentary microfacies include channel,channel bar,pond and overflow deposits. Two stratigraphic cycles of increasing and decreasing accommodation/sediment supply (A/S) regimes are identified. The two midterm cycles are divided into several shortterm cycles. This paper summarized the characteristics of baselevel cycle, and clarified how the stratigraphic stacking pattern changed with different A/S ratios. The connectivity of channel sand is good under low A/S ratio and vice versa. The thickness of overflow deposits can be seen as the judgment basis of accommodation as it increases with rising A/S ratio.

Key words: braided river, outcrop, sedimentary characteristic, baselevel cycle, stacking pattern, A/S ratio, overflow deposits