Significance of Monodiexodina (Fusulininacea) in geology of Peninsular Malaysia

Abstract

Monodiexodina sensu stricto is a very rare genus of the Fusulinacea which was found in the Permian deposits. Its distribution is restricted to a narrow sliver extended from the central of Afghanistan in the west to Japan, Eastern Russia and Malaysia in the east. Only three species of the genus have a wide distribution in the south Asia and Southeast Asia. They are Monodiexodina sutschanica, Monodiexodina shiptoni and Monodiexodina kattaensis. Their restricted geographic distribution may reveal their paleobiogeographic province which is very important for establishing paleogeography. Monodiexodina shiptoni is a good index fossil which was used as a zonal marker for the Artinskian, late Early Permian. The geographic distribution of the species suggests that the species were warm-water species which occupied the tropical or subtropical shallow seas. In Sibumasu block, only Monodiexodina sutschanica and Monodiexodina shiptoni were found in either limestone or calcite cemented sandstone which overlies the pebbly mudstone of glacio-marine origin. In East Malaya block, two species of Monodiexodina were found in the Sumalayang limestone. They are Monodiexodina kattaensis and Monodiexodina shiptoni. They are associated with many species of Fusulinacea. Their occurrence may give some clues to the evolution of the paleoclimate and tectonic history of the two blocks during the Permian. Monodiexodina is a very rare genus of the Fusulinacea. It first appeared in the Middle Cordilleran region, became widespread during the Sakmarian, and restricted to the Tethyan region during the Artinskian and the early Late Permian (Ross, 1967). There are two groups of Monodiexodina. The first is Monodiexodina sutschanica group which consists of Monodiexodina sutschanica (Dutkevitch), Monodiexodina shiptoni (Dunbar) and Monod'iexodina matsubaishi (Fujimoto) which is considered as Monodiexodina proper. The second is Monodiexodina kattaensis group which includes Monodiexodina kattaensia (Schwager), Monodiexodina bispatulata Williams, Monodiexodina prolongata (Berry), Monodiexodina steinmanii (Dunbar and Newell), Monodiexodina wanneri (Schubert) and Monodiexodina wanganensis Sossina. This group is morphologically intermediate between Monodiexodina strict sense and genus Parafusulina (Choi, 1973). Recently, two species of Monodiexodina, Monodiexodina sutschanica and Monodiexodina shiptoni (plate 1) were discovered from the calcareous sandstone bed of the top part of Kubang Pasu Formation, at the excavation site of Timah-Tasuh Dam in Perlis (Basir Jasin and Koay, 1990). The