Detachment and Accretion‐Related Syn‐Rift Seaward Dipping Sequences in the NW South China Sea

ABSTRACT Seaward‐dipping sequences (SDS) are typically observed in sediment‐driven progradation of slope deposits in post‐rift sequences, or along magma‐rich rifted margins, where they are primarily formed by subaerial lava flows and referred to as seaward dipping reflections (SDRs). However, new seismic reflection data from the sediment‐rich northwestern South China Sea (NW‐SCS) reveal the existence of SDS in sediment‐rich syn‐rift sequences, here referred to as syn‐rift sedimentary SDS. Based on a detailed tectono‐stratigraphic analysis, we describe how these syn‐rift sedimentary SDS differ from magmatic SDRs and propose a conceptual model for their formation. We show that the formation of these sequences is most likely controlled by a combination of high sediment supply rates, rapid subsidence and creation of horizontal accommodation space, first along large‐offset detachment faults and later, during breakup, by magmatic accretion. While inner magmatic SDRs typically form in subaerial conditions above continent‐dipping faults, we suggest that syn‐rift sedimentary SDS can derive from turbiditic flows in a relatively deep‐water environment above oceanward‐dipping detachment faults and/or interfinger with magmatic additions. Finally, we discuss the implications of syn‐rift sedimentary SDS for the interpretation of rifted margins in general.