Neogene stratigraphy and paleoenvironments of China

Abstract

Neogene deposits are widely distributed in north and west China, whereas in southeast China they are confined to isolated basins. The Neogene in China is predominated by non-marine facies and marine deposits are limited to the Leizhou Peninsula, some islands and continental shelves, although Miocene brackish-water deposits were encountered in Xinjiang, northwest China, and a very brief marine transgression took place in north China near the end of the Pliocene. Non-marine Neogene deposits in China are largely fluvial and lacustrine in origin and composed of mudstones, sandstones and conglomerates with local occurrences of lignites and diatomites. The maximum thickness may exceed 2000 m (e.g. the Qaidam Basin). A rich fauna and flora have been found in many localities and the most famous are the Middle Miocene diatomites at Shanwang, Shandong Province, with unusually well preserved vertebrate and plant fossils. A total of 7 mammal stages have been distinguished in China (5 in the Miocene, 2 in the Pliocene) and tentatively correlated with the European stages. A major realignment of climatic zones occurred before the Paleogene/Neogene boundary, when the Paleogene climatic zones, with a NW-trending broad arid zone across the whole of China, was eliminated and the arid zone moved to northwest China, presumably indicating the onset of the monsoon circulation system. During the last few years, the marine Neogene has been intensively studied in the Leizhou Peninsula and the three major sedimentary basins off the south China coast: the Beibu Gulf (Gulf of Tonkin) Basin, the Zhujiangkou (Pearl River mouth) Basin and the Yinggehai Basin. This sequence is over 3000 m thick, ranges from the Oligocene to the Pleistocene and consists of grey mudstones, sandstones and conglomerates, interbedded with biogenic deposits such as reef limestones and sandy chalk. At least 6 foraminiferal assemblages can be recognized in the three basins: the Psudohastigerina micra assemblage from the Oligocene, the Globigerina ciperoensis-Cassigerinella chipolensis assemblage from the Lower Miocene, the Globoratalia siakensis-Orbulina suturalis assemblage from the Middle Miocene, the Globigerina nepenthes-Globorotalia acostaensis assemblage from the Upper Miocene and/or Lower Plicoene, the Globorotalia tosaensis- Globigerinoides extremus assemblage from the Upper Pliocene and the Globorotalia truncatulinoides assemblage from the Quaternary. The nannofossil succession and larger foraminiferal faunas confirm the ages. The tropical nature of the Neogene faunas is revealed by the occurrences of large foraminifers and warm-water species of other groups. The transgression cycles are controlled by tectonic processes during the Oligocene and Early Miocene, but later by eustatic movements.