New data on the continental deposits from the Cao Bang Basin (Cao Bang-Tien Yen Fault Zone, NE Vietnam) - biostratigraphy, provenance and facies pattern

ANNA WYSOCKA^1*, PHAN DONG PHA^2,3*, EWA DURSKA¹, URSZULA CZARNIECKA⁴, DO VAN THANG^{1, 2}, ANNA FILIPEK¹, NGUYEN QUOC CUONG⁵, DANG MINH TUAN^3,5, NGUYEN XUAN HUYEN⁵ and HOANG VAN THA⁵

¹ Faculty of Geology, University of Warsaw, Żwirki i Wigury 93, PL-02-089, Warsaw, Poland. E-mail: anna.wysocka@uw.edu.pl

² Institute of Marine Geology and Geophysics, Vietnam Academy of Science and Technology, Building A27, 18 Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam. E-mail: phandongpha@gmail.com

³ Graduate University of Science and Technology, Vietnam Academy of Science and Technology, Building A21, 18 Hoang Quoc Viet Str., CauGiay Distr., Hanoi, Vietnam.

⁴ Department of Geosciences, University of Oslo, P.O Box 1047 Blindern, 0316 Oslo, Norway.

⁵ Institute of Geological Sciences, Vietnam Academy of Science and Technology, 84 Chua Lang Str., Dong Da Distr., Hanoi, Vietnam.

* corresponding authors

ABSTRACT:

Wysocka, A., Pha, D.P., Durska E., Czarniecka, U., Thang, D.V., Filipek A., Cuong, N.Q., Tuan, D.M., Huyen, N.X. and Tha, H.V. 2018. New data on the continental deposits from the Cao Bang Basin (Cao Bang-Tien Yen Fault Zone, NE Vietnam) – biostratigraphy, provenance and facies pattern. Acta Geologica Polonica, 68 (4), 689–709. Warszawa.

The Cao Bang Basin is the northernmost of the basins related to the Cao Bang-Tien Yen Fault Zone in northern Vietnam. The basin is filled with a thick series of continental deposits. However, the exact age of the sedimentary basin infill has been under discussion for a long time. Because of new published data, the authors have decided to revisit this basin. Palynological data has allowed us to assign the Cao Bang Basin infill to the Lower Oligocene PC1 complex of the Shangcun Fm. (southern China). Among the saccate grains of gymnosperms, the domination of Cathaya and Pinus was observed, whereas angiosperms are represented by Carya, Celtis, Hammamelidaceae, Ulmus and also Pterocarya, Quercus, the Castanea–Castanopsis–Lithocarpus group, and the Loranthaceae. Among pteridophytes occur Laevigatosporites, Osmundaceae, and Pteris. The sedimentological features of the Cao Bang Basin are distinct from those of other basins from the Cao Bang-Tien Yen Fault Zone. The basin is filled with a wide variety of clastic deposits, from some of coarse-grained, alluvial-fan origin, through sandy beds of fluvial origin up to fine, organic-rich lacustrine deposits. The coarse-grained lithofacies are built of clasts derived mainly from local sources. The sandstones from the basin equally are submature or immature. They contain a lot of lithoclasts, the composition of which depends on the sample location within the basin. The potential source area is composed of older sedimentary units and of granitic rocks. The geochemical samples studied reflect the geochemical composition of silicic source rocks with only a minor contribution of basic components. The succession that fills the basin is interpreted as a typical fill for relatively long-lasting evolving half-graben or strike-slip basins. Moreover, the basin is partly occupied by a subsequent present-day sedimentary basin of Quaternary age.

Key words: Continental environments; Pollen and spores; Provenance; Palaeogene; Cao Bang; Vietnam.