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 (similar to 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 (similar to 30 Ma) and IODP Site U1435 (similar to 34 Ma), suggesting a 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 gradient.

Automated summary

The study focused on the rift and sediment sources of the Palawan microcontinental block, revealing a breakup unconformity date of around 33-32 Ma and a conjugate relationship between the Palawan microcontinental block and the Pearl River Mouth Basin.