Abstract

In Tertiary basins, biostratigraphy can provide much more information about sequence stratigraphy than the identification of condensed sections using foraminiferal, nannofossil and dinocyst abundance and diversity peaks. Palynology may also allow systems tracts to be differentiated by consideration of miospore assemblages which may reflect changes in the character of coastal geomorphology during periods of sea level fall, sea level rise or stillstand.

During phases of sea level fall, lower coastal plain facies, and their associated plant communities, will be of minimal extent, whereas during phases of rising sea levels, successive drowning of coastal areas often results in a marked expansion in the representation of brackish water plant communities, such as mangroves. Stillstand phases may be marked by coastal progradation and the expansion of upper coastal plain facies and associated freshwater swamp plant communities. Also, in cases where sea level fluctuations are glacio-eustatic, and hence climatically driven, it may be possible to differentiate highstand from lowstand scenarios through consideration of evidence for climatic change.

Palynological studies of well-dated Quaternary sections from the Southeast Asian area provide excellent analogues which can be used to demonstrate the character of terrestrially derived miospore assemblages during periods of known sea level fall (e.g. during the time immediately following the last interglacial, after 110,000 yrs BP), sea level lowstand (e.g. during the last glacial maximum, 25,000 - 17,000 yrs BP), or from the last sea level rise during the early Holocene, (10,000 - 6,000yrs BP) and subsequent sea level highstand (6,000 - 0 yrs BP). On the basis of these analogues, a generalized model is proposed which can be applied to the identification of systems tracts within many Southeast Asian basins, as well as Neogene basins from other tropical regions.

Using the proposed model, the biostratigraphic character of each systems tract will be discussed by reference to Neogene examples from the Niger Delta and Southeast Asia.