14:00 〜 14:15
[MIS28-02] Early Cretaceous anti-tropical radiolarians of from Tibet at the breakup timing of Gondwana
キーワード：早白亜、Parvicingulids、両極分布、ガンバナ
The Yarlung–Tsangpo suture zone, which contains remnants of the ancient Neotethys Ocean, marks the tectonic boundary between Eurasia and India. South of the suture lies the Tethyan Himalaya, composed of sedimentary and volcanic rocks. Early Cretaceous marine sediments preserved in the northernmost Indian passive margin contain abundant radiolarians. Coeval radiolarian faunas and their paleobiogeographical affinities from the southern Tibet and Argo Basin have the potential to elucidate the northern extent of Greater India and the breakup of East Gondwana.
Parvicingulids, which are useful indicator of mid- to high-latitude deposition during the Jurassic to the Early Cretaceous, are common from radiolarians in southern Tibet and Argo Basin. However, the antitropical distribution of Parvicingulids have not been systematically analysed and their paleobiogeographical implications are still unclear. The locations, sedimentary setting, age assignment of species belong to Parvicingulidae are summarized to elucidating the time of their origin and, accordingly, outline how their antitropical distribution developed.
Tethyan species dominant in Gyangze during the Berriasian to Valanginian (145–132 Ma) indicate the deposition position of paleobiogeographical Tethyan Province. The change of radiolarian assemblages in Gyangze from Tethyan species dominant to Parvicingulids dominant occurred around Valanginian (140–130 Ma). The occurrence and dominance of Parvicingulids at Gyangze around 140–130 Ma indicate a later influx of southern paleolatitude origin circumantarctic current to the west. The influx of circumantarctic current transported to Zhongba around 130–125 Ma and the influence became weaker according to the dominance of Tethyan species with low abundance and diversity of Parvicingulids. Wide distribution of Parvicingulids in West Timor (Munasri and Sashida, 2017), Gyangze, Kangma, and Zhongba around 130 Ma corresponds to the breakup at 130 Ma and the Greater India’s anticlockwise rotation from 136 to 120 Ma.
References:
Munasri and Sashida (2017) Earth Evolution Sciences, 12, pp. 3-12
Parvicingulids, which are useful indicator of mid- to high-latitude deposition during the Jurassic to the Early Cretaceous, are common from radiolarians in southern Tibet and Argo Basin. However, the antitropical distribution of Parvicingulids have not been systematically analysed and their paleobiogeographical implications are still unclear. The locations, sedimentary setting, age assignment of species belong to Parvicingulidae are summarized to elucidating the time of their origin and, accordingly, outline how their antitropical distribution developed.
Tethyan species dominant in Gyangze during the Berriasian to Valanginian (145–132 Ma) indicate the deposition position of paleobiogeographical Tethyan Province. The change of radiolarian assemblages in Gyangze from Tethyan species dominant to Parvicingulids dominant occurred around Valanginian (140–130 Ma). The occurrence and dominance of Parvicingulids at Gyangze around 140–130 Ma indicate a later influx of southern paleolatitude origin circumantarctic current to the west. The influx of circumantarctic current transported to Zhongba around 130–125 Ma and the influence became weaker according to the dominance of Tethyan species with low abundance and diversity of Parvicingulids. Wide distribution of Parvicingulids in West Timor (Munasri and Sashida, 2017), Gyangze, Kangma, and Zhongba around 130 Ma corresponds to the breakup at 130 Ma and the Greater India’s anticlockwise rotation from 136 to 120 Ma.
References:
Munasri and Sashida (2017) Earth Evolution Sciences, 12, pp. 3-12