A Late Devonian to Early Carboniferous radiolarian fauna is present in chert and siliceous shale of a chert-clastic section along the Khong River, Pak Chom area, at the Thai-Lao border of northeastern Thailand. The radiolarian fauna is composed of Stigmosphaerostylus variospina, Astroentactinia stellata, Astroentactinia multispinosus, Archocyrtium wonae, Archocyrtium riedeli, and other species and corresponds to the Famennian (Late Devonian) to Tournaisian (Early Carboniferous) radiolarian fauna reported from northwestern Europe, Australia, northern and southern Thailand, and southern China. Ten radiolarian species belonging to four genera including one unidentified genus are investigated. The radiolarian-bearing sequence was probably deposited in a pelagic or hemipelagic environment within the Paleotethys Ocean during Late Devonian to Early Carboniferous time. Furthermore, this chert-clastic section of Pak Chom area is thought to be deposited on the Nakhon Thai Block and subducted beneath the Indochina Block. This suggests that the age of subduction and accretion of the Naknon Thai Block is thought to have occurred at least after Early Carboniferous indicated by the occurrence of Late Devonian to Early Carboniferous radiolarians.
A Middle Triassic radiolarian fauna is present in the siliceous rock section at the Nan area along the Nan-Uttaradit suture zone, northern Thailand. The radiolarian fauna is composed of Triassocampe deweveri, T. nishimurai, Annulotriassocampe campanilis, Cenosphaera igoi, and other species and corresponds to the Anisian (Middle Triassic) Triassocampe deweveri fauna reported from Japan, Hungary, Italy, Austria, Far East of Russia, and northern and eastern Thailand. More than fifteen radiolarian species belonging to eight genera are investigated. The radiolarian-bearing rocks were probably deposited in a pelagic environment within the Nan-Uttaradit back-arc basin between the Simao and Indochina blocks during Middle Triassic time. This suggests that the Nan-Uttaradit back-arc basin, the Palaeo-Tethys ocean and Panthalassa ocean were probably connected by seaways at this time and might have shared the same oceanic circulation system. Furthermore, the complete closure of the Nan-Uttaradit back-arc basin between the Simao and the Indochina blocks is thought to have occurred at least after the Middle Triassic.
Lower Permian (Asselian to Sakmarian) radiolarians and conodonts are identified from the bedded chert of the Chanthaburi area along the Sra Kaeo Suture Zone in eastern Thailand. The radiolarian and conodont-bearing bedded chert including radiolarian species such as Parafollicucullus bulbosus, P. lomentarius, P. u-formus, Pseudoalbailella scalprata, and others is exposed as large-size exotic blocks within the Thung Kabin mélange. This radiolarian fauna further includes Triplanospongos musashiensis, Triaenosphaera minuta, Latentifistula texana, Latentibifistula asperspongiosa and others, which have previously been reported from the Middle to Upper Permian. Except for these Middle to Upper Permian species, this radiolarian fauna is quite similar to those from Japan, Oregon, South China, West Texas, Cis-Urals and Central and Northeastern Thailand. Asselian to Sakmarian conodont faunas represented by Streptognathodus constrictus which have been reported from the Southern Urals and South China, and several sponge spicules are also contained in this bedded chert. Occurrence of these Lower Permian conodonts is the first record from the Sra Kaeo Suture Zone. This radiolarian- and conodont-bearing bedded chert was probably deposited in the Palaeotethys /or Palaeotethyan back-arc basin which is thought to have been a pelagic environment at low latitudes of the Southern Hemisphere.
The Khok Kruat Formation is the upper part of the Khorat Group, which consists of upper Lower Cretaceous non-marine sedimentary rocks in northeastern Thailand. Many dinosaur footprints have been known from the upper Lower Cretaceous (Aptian–Albian) Khok Kruat Formation at the Huai Dam Chum (Tha Uthen) site, northeastern Thailand. Approximately 600 tracks occur in thin mudstone layer of the northern part of the outcrop at the Huai Dam Chum track site. Two types of footprints, small-sized theropod and crocodylomorph are imprinted with mud cracks and ripple marks on the thin mud layer. Most of footprints are referred to cf. Asianopodus, and are imprinted by small-sized theropoda, probably ornithomimosauria. Theropod tracks are mainly separated into two groups, Group A and Group B. From ichnological viewpoints, the small-sized theropod track assemblage indicates the herd behaviour and its idiosyncratic group composition. In particular, the histogram of size-frequency measurements of Group A shows the anomalous bimodal distribution. We consider that there are two hypotheses; the first one is due to the male-female difference, and the second is a result of the different growing stage.
