LOWER JURASSIC

Introduction

In recent years, many publications on Lower Jurassic ammonites from the western side of the Pacific Ocean have been published, and together with earlier publications they provide a much more complete understanding of regional biostratigraphy (Table 12.1). Various Russian authors have described Lower Jurassic ammonites from eastern and northeastern Asia, and a detailed biozonation has been developed based, for the most part, on ammonites; for summaries, see Repin (1984) and Krymholts, Mesezhnikov, and Westermann (1988). Lower Jurassic ammonites are rare in most areas in Japan, and only a few papers have been published since the synthesis by Arkell (1956). A summary, regional zonation for part of the Lower Jurassic, along with range charts, has been provided by Hirano (1973, 1985) and Sato and Westermann (1985, 1991). Lower Jurassic ammonites from the Pacific border of southern China are mainly known from the Guangdong province, but only three Sinemurian assemblages have been established (Wang and Smith 1986). In Indochina, Lower Jurassic ammonites are mainly represented in Vietnam. All stages have been proved, but a detailed biozonation is not yet possible (Vu Khuc 1984). From Thailand (Mae Sot region), only late Toarcian ammonites are known (Braun and Jordan 1976). No Lower Jurassic ammonites have been described from the Malay Peninsula, the Philippines, or Sumatra. Some ammonites of Sinemurian and Toarcian age were found in Borneo (Krause 1896, 1911; Hirano et al. 1981).