Larger benthic foraminifera in Miocene carbonates of Indonesia

Abstract

Present day Southeast Asia represents the region that supports the most diverse marine ecosystems on Earth. The origin of this biodiversity is still unresolved, but it is proposed to be present at least since the Early Miocene. Therefore, the data acquired from the fossil assemblages may contribute to our understanding of this biodiversity hotspot. In this thesis Miocene larger benthic foraminifera (LBF) were investigated in order to provide new insights regarding their biostratigraphy and depositional paleonvironments. The focus of the research includes mixed carbonate-siliciclastic (MCS) systems of the Kutai Basin in East Kalimantan (Indonesia). Additionally, the study also includes localities from Bulu Formation (Central Java) comprising carbonate platform depositsto provide a comparative model with the blue-water systems. Until recently, MCS systems were considered to be environments inhospitable for carbonate producers compared to the blue-water marine systems, and hence were often neglected in biodiversity studies. However, recent studies reveal high biodiversity in these turbid water settings, including corals, LBF, algae, and bryozoans. The Kutai Basin was a host for the development of numerous MCS systems, with a peak of their deposition during the Miocene.Herein MCS systems are defined as in situ mixing, with the carbonate fraction consisting of autochthonous or parautochthonous death assemblages of calcareous organisms, accumulated on or within siliciclastic substrates. In these depositional systems LBF are important contributors to carbonate production, and combined with their high tolerance of terrigenous input, individually they are the most suitable taxa for paleoenvironmental reconstruction and interpretation. Based on the work from this study, a distribution model was proposed for LBF in Miocene carbonates of Indonesia, including the MCS systems, usually located in front or near the delta, but also for more sheltered environments without significant terrigenous input.By investigating LBF assemblages of Miocene MCS systems of the Kutai Basin, including their biostratigraphy, microfacies analysis, environmental reconstructions, and comparison with contemporaneous carbonate platform deposits, this research helps in untangling the origins of the Indo-Pacific biodiversity hotspot.