Cenozoic stratigraphy of Taiwan: Window into rifting, stratigraphy and paleoceanography of South China Sea

Abstract

Shallow marine sequences of the northern South China Sea (SCS) are uplifted and exposed by plate convergence in the Taiwan mountain belt. These deposits provide detailed geological information about the rifting event, stratigraphy, sedimentology, paleoclimate and paleoceanography of the shallow SCS to compare with what are recorded in the ODP 1148 deep-sea core. Seismic surveys and marine micropalentological studies show that Eocene sequences in the offshore Taiwan Strait and onland Taiwan mountain belt are all deposited in rifting basins and are covered unconformably by the Late Oligocene-Neogene post-rifting strata. Between syn-rifting and post-rifting sequences, there is a regional break-up unconformity throughout the island. Early Oligocene and Late Eocene strata are missing along the break-up unconformity equivalent to the T 7 unconformity in the Pearl River Mouth Basin off south China. This may suggest that the SCS oceanic crust could have initiated between 33 and 39 Ma. Neither obvious stratigraphic gap nor slumping features are found in the Oligocene-Miocene transition interval of Taiwan. This observation highly contrasts with what has been documented from the ODP 1148 deep-sea core. This suggests that the stratigraphic gap and slumping features could only be recorded in the SCS deep sea region, but not in the shallow shelf near Taiwan. Compared to the Middle Miocene paleoceanographic re-organization events in the SCS deep sea, the geological history of the Taiwan shallow sequence shows changes of in sedimentation and faunal composition. Due to the Antarctic glacial expansion at ~14 Ma, Middle to late Miocene strata of the Western Foothills show progressive regression sedimentations associated with a decrease of benthic foraminiferal abundance and a sharp faunal turnover event. Many Early-Middle Miocene endemic benthic foraminifers were extinct in 14-13 Ma and new benthic foraminifers of the Kuroshio Current fauna appeared from 10.2 Ma, comparable with new occurrence of Modern benthic foraminifers at 9 Ma in the Java Sea area. This reveals that the Western Boundary Kuroshio Current in the North Pacific could initiate from 10-9 Ma due to closures of the Indo-Pacific seaways by convergent tectonics between the Australian Continent and the Indonesian Arc in 12-8 Ma. Subduction of the SCS oceanic lithosphere since the Middle Miocene resulted in formation of the Hengchun Ridge accretionary prism and the North Luzon Arc. Occurrence of these two bathymetric highs (2400 m) since the Middle Miocene and closures of the inter-arc passages in the North Luzon arc in the last 3.5 Ma would control the water exchanges between the West Pacific and the deep SCS. Accordingly, the tectonic evolution in the Central Range-Hengchun Peninsula accretionary prism and the arc-forearc Coastal Range not only control directly the route for water exchanges between the West Pacific and the SCS, but also indirectly shows a great influence on the geochemistry of deep SCS waters. The latter is best shown by much negative carbon isotope v...

The first record of Eocene tuff in a Paleogene rift basin near Nantou, Western Foothills, central Taiwan

“…It contains Late Middle Eocene nannoplanktons (Zone NP16) with the reworked Paleocene and Cretaceous fossils, similar to what have been found in the underlying Discocyclina-bearing Chungliao Formation (Zones NP14-15; Middle Eocene; Huang et al, 2012Huang et al, , 2013. The reworked Paleocene and Cretaceous nannoplanktons in the Pinglin Tuff could be derived from the pre-rift basement in hosts or Early Tertiary syn-rift basins onshore the Peikang Basement High and its offshore counterpart.…”

“…The unconformity between the Latest Oligocene Wuchihshan Formation and the Middle Eocene Pinglin Tuff corresponds to the regional break-up unconformity between the post-and syn-rift sequences related to the opening of the South China Sea in the Early Tertiary (Huang et al, 2012). This regional break-up unconformity corresponds to the Puli Movement in the Taiwan region (Chang, 1955(Chang, , 1972Huang et al, 2012). This is the first document to show that in the Western Foothills unconformably below the Late Oligocene Wuchihshan Formation, there are the Eocene strata and also shows the first discovery of a Paleogene rift basin exposed in the Western Foothills.…”

“…The sequence in the Nantou area, Western Foothills, is correlated with the rift history what have found in the Taiwan Strait-Pearl River Mouth basin in the NE South China Sea. The unconformity between the Latest Oligocene Wuchihshan Formation and the Middle Eocene Pinglin Tuff corresponds to the regional break-up unconformity between the post-and syn-rift sequences related to the opening of the South China Sea in the Early Tertiary (Huang et al, 2012). This regional break-up unconformity corresponds to the Puli Movement in the Taiwan region (Chang, 1955(Chang, , 1972Huang et al, 2012).…”

“…Similar Eocene or Paleocene volcanics unconformably beneath the Late Oligocene-Miocene post-rift sequence were also documented in the Penghu Basin in the Taiwan Strait (Hsiao et al, 1991;Lin et al, 2003), the Peikang Basement High in the Coastal Plain onshore Taiwan (Yuan et al, 1985), and the Pearl River Mouth Basin offshore southern China (Li and Rao, 1994;Zou et al, 1995). The Paleogene eruptions are all tectonically related to the opening of the South China Sea (Huang et al, 2012). The break-up unconformity between the syn-rift and post-rift sequences marks the ''Puli Movement'' in the Taiwan area (Chang, 1955(Chang, , 1972Huang et al, 2012).…”

“…The Paleogene eruptions are all tectonically related to the opening of the South China Sea (Huang et al, 2012). The break-up unconformity between the syn-rift and post-rift sequences marks the ''Puli Movement'' in the Taiwan area (Chang, 1955(Chang, , 1972Huang et al, 2012). In the Borehole PC-1 on the Peikang Basement High, the thick tuff of the Shuangchi Red Beds (for at least 300 m thick; Lee, 1962;Chiu, 1972;Yuan et al, 1985) at 1953 m deep has been dated as 44.1 ± 2.2 Ma (Middle Eocene) by using K-Ar dating method (Yuan, 1981).…”