Lithology-Based Sequence-Stratigraphic Frame-work and Sedimentary Evolution of the Cenozoic Succession in the Northeastern Nanpu Sag, China

The Nanpu Sag, located in the northeast of North China Craton, is a Meso-Cenozoic petroliferous sag. Various models have been proposed to reveal the distribution of sand bodies and hydrocarbon accumulation regularity, but... [ view full abstract ]

The Nanpu Sag, located in the northeast of North China Craton, is a Meso-Cenozoic petroliferous sag. Various models have been proposed to reveal the distribution of sand bodies and hydrocarbon accumulation regularity, but controver-sies remain. To address this issue, we present a lithology-based sequence-stratigraphic framework of Liuzan Area in the Nanpu Sag to figure out the complex spatial and tem¬poral facies relationships. Based on the interpretation of the seismic reflection termina¬tions, wireline-log stacking patterns and lithological data, six three-order se¬quences were identified in the Shahejie Formation. Seismic reflectors typically coin¬cided with key sequence-stratigraphic surfaces. Sequence 1 and sequence 2 were mainly dominated by sub-parallel seismic reflection configuration, indicating the lacus¬trine deposits. The brush progradational reflection configuration recognized in the margin of study area demonstrated the fan-delta deposits. Different from the se¬quence 1 and sequence 2, the sequence 3 to sequence 6 were featured by large prograda¬tion refection configuration along the source direction, and mound or lenticu¬lar seismic reflection configuration perpendicular to the source direction. These seis¬mic reflection configurations indicated multi-stages fan-delta deposit systems. Sequence 3, which was used layer flattening to recover paleogeomorphologic feature, is composed of fan delta and lacustrine sedimentary environments controlled by northwest sources. In sequence 4, the delta-front facies, which is affected by clastic source in northeastern of region of interest, pinching out into delta-slope shales show a clear prograding pattern, with southwestward thinning and downlap onto sequence boundary 4. Sequence 5 and sequence 6 controlled by east sources, is developed a finer fan delta than which have formed earlier. In each depositional sequence, parasequences can be grouped into retrogradational parase-quence and progradational parasequence based on the stacking patterns. The sand-shale ratio in retrogradational parasequences decreased upward which indicated the expansion of the lacustrine facies. The progradational parasequences were domi-nated by coarse-grained clastic deposits, and developed the thicker sandstone com-pared to the retrogradational parasequences. The establishment of the high-resolution sequence stratigraphic framework emphasizes the reservoir potential of the terrestrial lacustrine sediments and provides a useful guidance to identify the potential areas for hydrocarbon exploration.