The Solomon Sea is a semi-enclosed oceanic basin bordered by technically active land masses: its morphology is dominated by an arcuate trough, the New Britain Trench, which bounds the basin on its northern side and is over 8000 metres deep. Density of soundings is sufficient to reveal a large scale left-lateral displacement near the western end of the New Britain Trench; this appears to be a continuation of the onshore Markham-Ramu Lineament. The same structure controls the position of the Markham submarine canyon, which is the major conduit feeding sediment to the ocean basin. No continental shelf is developed along the northern margin of the Huon Gulf owing to the strong and continuing uplift of the Huon Peninsula, which lies within the Northern New Guinea Arc structural province. South of Lae, however, a narrow continental shelf is present. Seismic reflection profiles reveal that this shelf is a geologically young constructional feature, composed in its upper levels of a coalescing series of deltaic deposits. In some areas these can be seen resting directly on non-sedimentary basement. Several submarine canyons cross the shelf and each is closely related to a large river onshore. The seismic records clearly show truncation of strata by the canyon walls: however, it is postulated that upgrowth of the shelf around the canyons, with occasional slumping along the rims, as well as axial downcutting by abrasive sediment flowage, have controlled the formation of the canyons. Their steep axial gradients, which average about 5° compared with the shelf surface which slopes seaward at only 1°, are taken to indicate that the canyons were initiated before the Pleistocene and have maintained their courses during the upward and outward growth of the deltaic deposits forming the present day continental shelf.
