Abstract: The obvious sedimentary differences can be found between the upper and lower parts of the Karamay Formation in the north of Hongshanzui. To determine the sedimentary characteristics of the Karamay Formation, the seismic, core logging, and analytical data were used to analyze the rock and mineral characteristics, typical lithofacies, and sedimentary facies of the Karamay Formation. The results show that the lower Karamay Formation is characterized by the braided river deposits with obvious traction-current deposition, which is mainly composed of braided channel (Gi → St → Sp → (Sh) → Md), braided bar (St→Sp↔Sm), and alluvial plain (Mr↔Md → Fr). The channel sand-bodies are banded and mostly isolated from thick mudstone. The upper Karamay Formation is dominated by fan-delta with debris flow, density flow and tractioncurrent deposits. The braided channel (Gmm→Gcm→Gi→Sh), braided distributary channel (Gcm→Gi↔Gt) and braided bar (Gp↔Gi→Gcm) are developed in the fan-delta plain. The underwater distributary channel (Gi→Gt→Gp→St), mouth bar (Md→Sp↔Sw) and interdistributary bay (Md↔Sc) are developed in the fan-delta front. The thick stacked sandy conglomerate bodies are scours and overlap with each other and also characterized by good connectivity and broad distribution. The transformation from the braided river to fan-delta in the Karamay Formation is mainly controlled by the forwarded provenance system and increased supply capacity, the transition of the paleoclimate from arid and semi-arid to sub-humid and humid, and the lake level rise. 

Key words: braided river, fan-delta, sedimentary sequences, depositional evolution, Karamay Formation, North Hongshanzui area