From uplift to deposition: Tectonic controls on source-to-sink evolution during ophiolite collision in East Sulawesi. Insights from the Batui Fold-Thrust Belt

The island of Sulawesi in eastern Indonesia has been shaped by multiple periods of complex tectonic interaction and volcanism, driving recent scientific interest in regional geohazards (e.g., earthquakes and landslide-drive tsunamis) and the formation of natural resources (e.g., natural hydrogen). Despite this, fundamental questions about the geological evolution of Sulawesi remain understudied, such as the timing and style of the collision between the Banggai-Sula Microcontinent and the East Sulawesi Ophiolite. This collision zone has been largely overlooked due to the remote and rugged terrain along the suture. Here, we present new fieldwork data from the Batui Fold-Thrust Belt of the East Arm of Sulawesi, along with remote sensing, petrographic, and biostratigraphic data to reveal the stratigraphic and structural features of this suture zone, highlighting the key depositional environments that developed before, during, and after collision.

Fieldwork, petrography, and biostratigraphy data reveal dismembered upper mantle and lower crustal rocks of the East Sulawesi Ophiolite in tectonic contact with Middle to Late Miocene shallow marine limestone of the Salodik Formation. These limestones interfinger with coeval siliciclastic rocks of the Poh Formation recording a transition from fore- and back-reef environments to a foreshore setting. These rocks are overlain by conglomerates of the Pliocene Bongka Formation that was deposited in a disconformable contact atop the East Sulawesi Ophiolite and marks final merging of the Banggai-Sula microcontinent. Crucially, the Middle to Late Miocene age of the Salodik Formation, together with reworked Eocene foraminifera, indicates uplift and progressive reef closure prior to renewed shallow-marine deposition. This has not been previously recognised from this formation elsewhere in Sulawesi during NW-directed Miocene collision. These interpretations are further supported by SE-verging structures in the hanging wall of the Batui Fold-Thrust Belt, which defines the main regional suture zone. By constraining the timing of uplift and reef shutdown, this study defines the source-to-sink boundary conditions for sediment generation, transport, and deposition during ophiolite collision in eastern Indonesia.