At all sites, the most common sedimentary structures are parallel laminations in the fine-grained facies, together with interbedding between fine-grained sediments and sandstones observed both at meso-and microscales (Pl. P1, figs. 4, 5).
As also pointed out by the Shipboard Scientific Party (1999), sedimentary structures evidently linked to sediment remobilization by turbidity currents are very common in Holes 1108B and 1116A. In particular in some sandstones, high-angle tabular cross-lamination is present (Cores 180-1108B-9R and 10R) and classic Bouma (Bouma, 1962) sequences are prominent features (e.g., interval 180-1108B-24R-2, 4-36 cm) (Pl. P1, fig. 6). In Hole 1116A, cross and convolute laminations in claystones and siltstones (Cores 180-1116A-1R through 4R) and in fine- to medium-grained sandstones (Cores 180-1116A-9R through 18R) are locally present. Normal grading in sandstones is common in Hole 1108B and reverse grading also occurs. The presence in Holes 1108B and 1116A of so many structures linked to turbidity currents is probably due to destabilization of still unconsolidated sediments coming from Moresby Seamount (Pl. P1, fig. 2). Moreover, intraformational rip-up clasts at these sites indicate the presence of high-energy currents, which remobilized newly deposited sediment. On the other hand, low-angle cross-laminations and graded beds present locally in silty sandstones in Hole 1115C (Cores 180-1115C-15R through 20R) are probably linked to marginal bottom currents. Bioturbation is common, especially in clayey siltstones at the rift basin (Cores 180-1108B-16R through 21R) and in claystones at the northern margin sites (Cores 180-1115C-1R through 11R and Cores 180-1109C-10H through 39X).