ABSTRACT: Processes of Sedimentation in a Tropical Carbonate, Tidally-Dominated, Shelf Environment -- Torres Strait, Australia

Chris Jenkins, Peter Harris, Elaine Baker

Torres Strait is a tropical carbonate, tidally dominated continental shelf sedimentary environment. Sedimentation in the area is of practical interest because it is shallow (sill depth = 12 m) and it forms an important shipping seaway; siltation along the shipping route could cause major problems. It is also an environmentally important area since mining waste dumped into the Fly River may be affecting the Torres Strait ecosystem. Thus an understanding of processes affecting the dispersal and deposition of sediments in Torres Trait is of vital importance.

Strong tidal currents, which flow through narrow channels between coral reefs and islands, are associated with submarine sand dunes and linear sand banks, features well known from temperate settings such as the North Sea (Europe) and Nantucket Sound (USA). In the tropical Torres Strait environment, seasonally reversing wind-driven currents (max U₁₀₀ = 15 cm/sec) superimposed upon the tidal currents (max U₁₀₀ = 140 cm/sec) cause dunes up to 7 m in height to reverse their asymmetries semiannually.

As Torres Strait joins the Coral Sea basin (in the east) with the Gulf of Carpentaria/Arafura Sea (in the west), tidal waves propagating from both of these basins converge and interact in Tortes Strait. Because only about 30% of a tidal wave is transmitted through the Strait, a tremendous amount of tidal energy is dissipated here, giving rise to a semipermanent "turbidity maximum" in central Torres Strait. Examination of seabed and suspended sediment samples indicates that sediments are eroded from the bed and reworked in the central Strait and removed out of the turbidity maximum by ebb-flowing currents to depositional zones.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990