The Southeast Sulu Sea, a Neogene marginal basin with outcropping extensions in Sabah

Abstract

The geophysical, drill and dredge details of the Sulu Sea marginal basin allow a correlation with the Neogene geology of eastern Sabah. The basin is modelled to have resulted from early Miocene intra-arc rifting related to the SE-facing subduction system of the NW Celebes Sea. The early stages of the opening of the Sulu Sea were characterized by explosive volcanic activity, and the rifting resulted in extensive olistostrome deposits. These events are seen onland as the Ayer and Tungku formations, and the Kuamut and Garinono formations respectively. Uplift ofthe Crocker Formation to the west provided the source for major quartz sands deposited in Sabah within the Tanjong Formation, and a major delta flowing northeasterly near Sandakan fed the continentally-derived turbidites of the deep Sulu Sea. Since the ophiolitic complex of Sa bah pre-dates the late-Lower Miocene opening of the Sulu Sea marginal basin, it represents the ocean floor upon which was built the volcanic arc, rifting of which gave rise to the Sulu Sea. Remnants of this early Cretaceous and older ophiolitic basement therefore underlie and outcrop within the NW margin of the SE Sulu Sea (Labuk Valley through the Cagayan Ridge), as well as along the Sulu Archipelago, extending into Darvel Day and Ulu Segama. Evidence is presented to show that the ophiolite complex was locally uplifted and eroding in the early Cenozoic.