Stratigraphy and provenance of the Paleogene syn-rift sediments in central-southern Palawan: paleogeographic significance for the South China margin

The Palawan microcontinental block is thought to have separated from the South China margin due to seafloor spreading and opening of the South China Sea. However, it is uncertain when and from which section the Palawan microcontinental block rifted from the South China margin, and little is known about sediment routing across the rifted margin before continental breakup. To address these aspects we studied the biostratigraphy and provenance of syn-rift sedimentary rocks collected from the Panas-Pandian Formation in central-southern Palawan. Micropaleontological evidence indicates a Middle Eocene–earliest Oligocene (47.7–32.9 Ma) age for the Panas-Pandian Formation. Based on this and the oldest age of the post-rift Nido Limestone (~32 Ma), the breakup unconformity on the Palawan microcontinent block is dated around 33–32 Ma. This timing of breakup unconformity is close to that of the Pearl River Mouth Basin (~30 Ma) and IODP Site U1435 (~34Ma), suggesting the conjugate relationship between the Palawan microcontinental block and the Pearl River Mouth Basin. Trace fossils and benthic foraminifera from the Panas-Pandian Formation indicate a middle bathyal to abyssal environment on the continental slope of the South China margin. Multidisciplinary provenance analysis reveals that the Panas-Pandian Formation was derived from both local Mesozoic basement uplifts and the interior Cathaysia Block. It indicates that a paleo-Pearl River has been established at least since the Middle Eocene (47.7– 42.1 Ma) and could deliver sediments from the interior Cathaysia Block to the continental slope, across the wide rifted margin with a low topographic gradien

Evolution of arc‐continent collision in the southeastern margin of the South China Sea: insight From the Isugod Basin in Central‐Southern Palawan

The evolution of arc‐continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc‐continent collision, we studied the biostratigraphy and provenance of syn‐collisional sediments in the Isugod Basin in central‐southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5–5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene–lower Oligocene Panas‐Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at ∼11.5 Ma, implying collision onset before ∼11.5 Ma. The collision initiation in Palawan could be better constrained to ∼18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4–11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16–15 Ma, arc‐continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward