Continental Shelf [23] On the continental shelf two contrasting sedimentary environments were identified: (1) the modern Fly River delta and (2) a system of relict, incised valleys seaward of the delta. The transition between these two environments is shown regionally in Figure 2b and occurs at 40 m depth. The modern Fly River delta is prograding in response to sediment input from the Fly River and has been shown to be infilling valleys incised into the Gulf of Papua shelf [Harris et al., 1993; Crockett et al., 2008]. These valleys occur between 40–80 m depth and were not extensively modified during the Holocene sea level transgression and thus represent an insight into fluvial processes operating in the region during the last glacial maximum. The Kiwai and Umuda valleys (Figures 3c and 3d) represent two different, sedimentary systems. Crockett et al. [2008] interprets the Kiwai Valley as a relict, incised valley. The valley is relatively long (28 km) but narrow (0.8–1.1 km) and consists of three, steep sided, meanders. The Umuda Valley by contrast, is interpreted as a modern, alluvially influenced, coastal plain distributary channel because of its broad nature (28 km) and low relief (