Tectono‐Stratigraphic Controls on Cenozoic Southeast Asian Carbonates

Abstract

In Southeast Asia, Cenozoic carbonates commonly were initiated or terminated at times of tectonic change, and they are bound by unconformities. A review of the timing of several of the largest unconformities shows they correlate over wide areas. These unconformities divide the stratigraphic record of Sundaland into episodes, with times of rapid basinal re-adjustment separated by periods of relative stasis. These generalizations are true not only in the successions deposited during the dominantly extensional later Eocene to early Miocene, but also in the often-compressional middle Miocene and younger deposits, in which at least three phases of rapid tectonic and stratigraphic change can be correlated over multiple depocenters. A detailed review of many areas of Southeast Asia using quantitative biostratigraphic methods indicates that tectonism resulted in relative changes in sea level, with no indication that eustasy was an important driving force. The boundaries between these sedimentary episodes vary in their effect and distribution, depending upon the tectonic cause. As a consequence, there is no uniform subdivision of the stratigraphic record across the region, which precludes a simple Sundaland-wide classification of primary sedimentary sequences. This review concentrates on both event timing and rates of change within and between basins, especially those changes that initiated or terminated carbonate deposition. In addition, some short-lived carbonate buildups that developed during transitional periods are described. This review provides the beginnings of a new stratigraphic framework for the Cenozoic carbonates and related deposits of Southeast Asia. It requires an inductive analytical methodology, in contrast to the model-driven and deductive approaches that have been applied in recent years. This episodic stratigraphy approach includes integration of large amounts of analytical data, for which the Cenozoic tropical sediments of Southeast Asian basins are particularly well suited.