Cenozoic stratigraphy of Small Nggela Island, Solomon Islands — early Miocene deposition in a forearc basin followed by Pliocene patch reef deposition

Abstract

Most of the sedimentary rocks of Small Nggela are early Miocene in age. In the north, uniform volcaniclastic arenite (the Siota Beds) crops out. Much of the central, western, and eastern parts of the island contain diverse strata including pillow lava, calcarenite, volcaniclastic arenite grit, and breccia (the Ghumba Beds). The Siota and Ghumba Beds, which are separated by a 1-1"5 km wide, east-trending ophiolite wedge, are considered to have been deposited in a forearc basin. The ophiolite wedge arrested the northward transport of coarse sediment and was emergent during the late Oligocene and early Miocene. The sediment and the ophiolite wedge are considered to have overlain a southward-descending Benioff zone.Well-bedded laminated arenite lacking basalt and rudite (the Ndandala Sandstone) is present in the south-western part of the island and is probably significantly younger than the underlying Ghumba Beds. A veneer of early-mid Pliocene limestone (the Florida Limestone), representing a patch reef environment, was deposited upon the Ghumba Beds after they had been folded.

Submarine‐fan deposited sandstone and rudite in a mid‐Cenozoic interarc basin in Maewo, Vanuatu (New Hebrides)

“…However, the dish structure noted by Winn & Dott is absent from the Lower Sarava Formation. Much thicker (20-30 m thick) graded breccia-arenite beds, also carrying rafted clasts, are known from deep water forearc basin deposits on Small Nggela, Solomon Islands (Neef, 1979).…”

Early Miocene extrusives and shallow intrusives from Small Nggela, Solomon Islands

“…Fossils indicate that the Ghumba and Siota Beds are largely Early Miocene in age (Neef, 1979). Most of the igneous rock present in the Ghumba Beds is tholeiitic pillow lava.…”

“…An ophiolite complex, with a K-Ar age of 36-38 Ma (Neef & McDougall, 1976) extends between Ghole and Hanuvaivine villages and it is considered to have acted as a topographic high during sedimentation in the Late Oligocene and Early Miocene (Neef & Plimer, 1979). Sediment N of the complex is uniform and consists largely of arenite (Siota Beds) whereas sediment S of the complex (the Ghumba Beds) is varied, containing much rudite and arenite and minor calcarenite and tholeiitic lava (Neef, 1979).…”