The Carboniferous of East Thailand - new information from microfossils

Abstract

In .1996 for the first time, Carboniferous microfossils were discovered in east Thailand, at a single limestone locality. In 1997, another locality of the same area yielded Early Carboniferous corals. Because of these two discoveries, a systematic search for microfossils has been carried out in all the limestone exposures of that area. Microfossils have been found almost everywhere; they are rare to . common. The fo ssils and the facies focus on an age ranging from Late Visean to Bashkirian. The Carboniferous sediments of East Thailand were not documented in the past. Their presence had been suggested by a few bryozoans found in shale (Nakinbodee et al., 1976). They consist of shale, silicified shale, siltstone, limestone, subordinate sandstone and conglomerate. In 1996, a first discovery of microfossils in the limestone of Khao Kradat (Fontaine et al., 1996), then of corals in a limestone exposure east of Khao Yai Mo Noi (Fontaine and Salyapongse, 1997) suggested that the distribution of Carboniferous limestone should be relatively extensive, especially because limestone bodies reaching thicknesses of 10 to 100 meters are scattered in the area. As a matter of fact, these limestone exposures contain locally fossils in abundance; microfossils have been found at several localities and are the subject of this paper. The sediments which have yielded the Carboniferous fossils crop out about 70 km east of Chonburi. Exposures are scattered in an area of about two hundred square kilometers, but they occupy only a small part of that surface. They are distributed in two land strips arranged in a northerly direction, about 2 km wide, parallel , discontinuous, 8 to 10 kill far apart from each other. They are represented by' small' hills, with the exception of Khao Yai which is very large and reaches 777 m in elevation above sea level.