THE SEDIMENTOLOGY AND STRATIGRAPHY OF THE JURONG FORMATION, SINGAPORE

Abstract

In the Triassic/Jurassic Era, the Malay Peninsula formed part of a small continental plate which experienced subduction from two opposite sides. This tectonic setting led to a widespread uplifting of the mountain range, as well as plutonic intrusions along the axes of the peninsula. This in turn gave potential for the development of back arc basins, of which the Jurong Formation was one. Generally three different environments can be identified: Shallow Marine Environment- These sediments are characterized by 20-50 m thick fining up cycles from massive sandstones through alternating Sandstone/mudstone into mudstones. Within the thicker cycle, a cyclicity on a smaller scale occurs which is 10-100 cm thick fining up cycles of graded sandstones through cross-lamination into parallel-laminated sandstones. These are interpreted as being storm-dominant shallow shelf environments. Beach environment- These consist of fining up 8-10 m thick cycles of mainly conglomerates and sandstones, with only thin mudstone sequences. It is most likely that these are beach and shoreline environments. Terrestrial environments- There are 4-6 m fining up cycling of dominantly trough stratified conglomerates and sandstones, occasionally interbedded with fine mudstones. These cycles are interpreted as being terrestrial, braided stream environment. The relationship between these environments cannot be established stratigraphically but the sequences suggest a back are basin gradually filling as a possible explanation for the development of the Jurong Formation. As a consequence the geology should reveal a coarsening tendency, as the depositional setting changed from offshore shallow shelves to beach and deltaic environments, and onshore to fluvial, braided stream environments.