Resumen de Late Cretaceous–Early Tertiary Continental and Lacustrine Basins of Hong Kong and Southeast China
R. Bernhart Owen
The coastal region of southern China and Hong Kongcontains several Late Cretaceous-early Tertiary continentalbasins (Figure 1) with red beds and laminated, lacustrinemud stones. Probable early Tertiary lake sediments crop out on the island of Ping Chau (Figure 2) in northeaster nHong Kong (Lai, 1991; Lai et al., 1996; Lee et al., 1991b),although their precise age has been the subject of a longdebate (Heanley, 1923; Williams, 1943; Davis, 1953; Ruxton,1960; Allen and Stephens, 1971; Peng, 1971; Lee, 1985,1987). The Ping Chau Basin covers 45 km2 and is an asymmetri chalf graben bounded by normal faults to the northwest and northeast (Lai, 1985). Two major sedimentary units are present. The Ping Chau Formation (about 210mexposed on the island of Ping Chau) lies at the basin center(Figure 2) and consists of thinly laminated, calcareous and dolomitic mudstone and siltstone, which dip 5-200 to the northeast. These overlie Port Island Formation red bedscomposed of siltstone, sandstone, and conglomerate.
A third sedimentary unit, the Kat 0 Formation, occursin a smaller basin to the west of Ping Chau (Figure 1).Thisunit consists of red, massively bedded, sedimentary brecciaand conglomerate laid down in fault-controlled alluvial fans. The precise stratigraphic relationships betweenthe Kat 0, Port Island, and Ping Chau Formations are uncertain due to poor exposure of boundaries and a lackof dating control .Several similar sedimentary basins of Late Cretaceous-early Tertiary age, with red beds or lacustrine mudstone and shale, also occur in southeast China (Gu andRenaut, 1994;Lai 1991). These include the Sanshui Dongguanand Xinhui Basins of Guangdong (Figure 1).Wang etal. (1985) suggested that the Guangdong Basins may have formed a single paleo lake during the early Tertiary, centeredon the modern city of Guangzhou (Figure 1).
The record in Guangdong is well preserved by the rocks of the Sanshui Basin. Lai (1991) notes that the lower Tertiary Buxin Group rests on red beds of the329Upper Cretaceous Dalang Shan Formation (Figure 3) and can be divided into three parts. The Paleocene First formation(the Xinzhang Formation of Lee et al., 1991b)consistsof 80 m of conglomerate overlain by 100-300 m of mudstone, marlstone and siltstone red beds with grayintercalations. The Second formation (Eocene) consists of100-300m of gray to black lacustrine mudstone, siltstone, and marlstone. The Third formation consists of 200-350mof Oligocene sandstone, siltstone, and mudstone.
Various attempts have been made to correlate the Sanshui(Guangdong) succession with the sequence recognized in Hong Kong at Ping Chau (Figure 3). Lai (1991) suggests that reddened mudstone, sandstone, and conglomerate of the Port Island Formation (Hong Kong) correlate with the Upper Cretaceous Dalang Shan Formation and that the Paleocene First formation of the Buxin Group (Tang et al.,1980)(Figure 3) correlates with sediments (visible on seismic sections) that are hidden below the sea floor near Ping Chau. According to Lai (1991),laminated mudstone and siltstone exposed on Ping Chau Island correlate with the Second formation, whereas the upper Ping Chau Formation sediments (also hidden below sea level) may equate to the Oligocene Third formation. The Kat 0 Formation's red conglomerate remains problematic, with Lai (1985) suggesting an Late Cretaceous age and Lee et al. (1991b) preferring a correlation with the Oligocene red beds of the Huayong or Sanshui Formations of the Sanshui Basin.
Similar continental successions are reported from other parts of Guangdong Province by Sun et al.(1981)and Song et al. (1986). Lee et al. (199Ib) note that this suggests the widespread development of oil shales, coals,and lake basins during the late Paleocene-Eocene in the southern coastal regions of south China.
