Abstract of ref. 1243:
Most of the sedimentary rocks of Small Nggela are early Miocene in age (dated by nannofossils and foraminifera). 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 limsteone (the Florida Limestone), representing a patch reef environment, was deposited upon the Ghumba Beds after they were folded. 