Sedimentary Characteristics and Evolution of Mesozoic in the Eastern Depression, North Yellow Sea Basin

Key words: 
• North Yellow Sea Basin /
• Eastern depression /
• Mesozoic /
• sedimentary facies /
• sedimentary evolution

Abstract: North Yellow Sea Basin is a typical Meso-Cenozoic superimposed fault basin, which has very weak exploration and research in the offshore of China. The Eastern Depression is the secondary building unit which has the best exploration foreground in North Yellow Sea Basin. According to the core observation and logging facies analysis, combined with 3D seismic data, it is considered that fan delta, braided-river delta, delta and lake developed in the Mesozoic in Eastern Depression. Restricted by structural evolution, there was different sedimentary evolution in different tectonic phase in Mesozoic. Middle Jurassic was in the period of initial graben faulting. The sedimentary types were mainly semi-abyss and abyss. There were few fan deltas in depression margin. Late Jurassic was in the period of faulting extension. The vertical lithological sequence was an integral depositional cycle of progradation-retrogradation. There were delta in north gentle slope and fan delta in abrupt slope in early stage. Owing to uprising of lake level, there developed undercompensation lake facies whose lithology is mainly dark mudstone. North gentle slope developed small-scale delta front. Early Cretaceous was in the period of faulting abortion, and there were two normal cyclic depositional sequences. The sedimentary types of each cycle were mainly fan delta, braided-river delta in lower part, and shore-shallow lacustrine upward.