Labuan Island represents the emergent part of a north-eastward plunging anticline. The stratigraphic succession at Labuan is made up of four formations: the Crocker Formation, the Temburong Formation, the Setap shale Formation and the Belait Formation. The sedimentological aspects of the Labuan stratigraphic succession have been studied by several authors but the stratigraphic relationships between the formations is still a matter of conjecture. In this paper we have undertaken and outcrop based (1) sedimentary facies analysis of the Middle Miocene Belait Formation and (2) inferred the mode of stratigraphic sequence building of the Oligocene-Miocene successions. In significant contrast to the tide-storm interactive shallow-marine Belait Formation of Brunei and Sarawak, the Belait Formation of the Labuan island is made up of a lower fluvial and an upper shallow marginal marine to shelf facies association. The sedimentary succession from the Crocker, Temburong, Setap Shale and Belait formations represents a marine regression either due to a relative sea-level fall (forced regression) or to sediment supply exceeding the rate of sea-level rise (normal regression). The ∼17 million years unconformity separating the fluvial facies association of the Miocene Belait Formation from the underlying shelfal sedimentary units (Oligocene Temburang and/or Setap shale formations) is a subaerial unconformity that is a consequence of rapid uplift and associated forced regression, and thus indicates the influence of regional tectonics on the mode of stratigraphic sequence building The change in paleocurrent pattern recorded by earlier researchers across the Oligocene-Miocene boundary also indicates tectonic tilt, and a change in sediment dispersal direction because of upliftment. The upper marginal marine facies association of the Belait Formation indicates transgression and the thick shelfal mudstone unit that overlies the marginal marine deposit indicates subsequent maximum flooding. Our sedimentological and stratigraphic analyses reveal that the shift in depositional environment during the Oligocene-Miocene transition is linked to regional tectonics and consequent sea level change and unrelated to paleoclimatic shift.

纳闽岛代表东北暴跌背斜的新兴部分。纳闽的地层演替由四个地层组成：克罗克组，滕布隆组，塞塔普页岩组和贝莱特组。几位作者已经研究了纳闽地层演替的沉积学方面，但是地层之间的地层关系仍然是一个推测。在本文中，我们进行了基于露头的（1）中新世中层贝莱特组沉积相分析，以及（2）推断了渐新世-中新世演替的地层层序构造模式。与文莱和砂拉越的潮汐风暴互动式浅海贝拉伊特编队形成鲜明对比，纳闽岛的贝拉伊特组由河床下部和上游边缘浅海相至陆架相组成。Crocker，Temburong，Setap页岩和Belait地层的沉积演替代表了海洋退缩，这是由于相对海平面下降（强迫退缩）或沉积物供应超过海平面上升速率（正回归）所致。将中新世Belait层的河流相与下伏的陆相沉积单元（渐新世Temburang和/或Setap页岩地层）相分离的约1700万年不整合是地下不整合的缘故，这是快速隆升和相关强迫退缩的结果，因此，这表明了区域构造对地层层序构造方式的影响。早期研究人员在渐新世—中新世边界上记录的古流型变化也表明了构造倾斜，并且由于隆升作用导致了沉积物扩散方向的变化。贝拉伊特组的上边缘海相相表明海侵，而覆盖在边缘海相沉积层上的厚陆架泥岩单元则表明随后发生了最大的洪水。我们的沉积学和地层分析表明，渐新世-中新世过渡期沉积环境的变化与区域构造和随之而来的海平面变化有关，与古气候变化无关。以及由于隆升改变了沉积物的扩散方向。贝拉伊特组的上边缘海相相表明海侵，而覆盖在边缘海相沉积层上的厚陆架泥岩单元则表明随后发生了最大的洪水。我们的沉积学和地层分析表明，渐新世-中新世过渡期沉积环境的变化与区域构造和随之而来的海平面变化有关，与古气候变化无关。以及由于隆升改变了沉积物的扩散方向。贝拉伊特组的上边缘海相相表明海侵，而覆盖在边缘海相沉积层上的厚陆架泥岩单元则表明随后发生了最大的洪水。我们的沉积学和地层分析表明，渐新世-中新世过渡期沉积环境的变化与区域构造和随之而来的海平面变化有关，与古气候变化无关。