A coal petrographic study of sediments, including coals, oil shale, and oil
source rocks, in the fossil fuel deposits of northern Thailand revealed ch
anges in alginite associations. In the Lower part of these Tertiary deposit
s, especially in the Fang oilfield, alginite A (a. Botryococcus sp.) was th
e only type of alga found. Later, the association of Botryococcus braunii,
Pila algae, thick-walled alginite B, and temperate palynomorphs were recogn
ized in many coalfields, as well as in the middle part of the deposits in t
he Fang Basin. Their ages were Late Oligocene (?) to Early Miocene. In the
upper part of the fossil fuel deposits, alginite B is dominant in many basi
ns, together with Botryococcus-related taxa such as Pila algae, Reinschia a
nd fresh-water-dwelling ferns. In the Mae Sod Basins Reinschia was found to
be dominant in the northern part, whereas lamaginite dominated in the sout
h, showing different environmental conditions in different parts of the bas
in during deposition. These different associations indicate changes in depo
sitional environments in northern Thailand; resulting from climatic and/or
sea level changes during Tertiary time, (C) 1999 Elsevier Science Ltd. All
rights reserved.