Larger benthic foraminifera in Miocene carbonates of Indonesia

Foraminifera are unicellular eukaryotic organisms that live individually autonomous in the sea (Hottinger, 2005). They form mechanically resistant tests, either by gluing material found in the environment or by secreting organic or calcareous shells. Along with the test, main characteristic of foraminifera are their pseudopodia emerging from the cell body through multiple apertures. Foraminifera are extremely abundant in marine sediments, which makes them useful in recent and fossil paleoenvironmental studies. The first simple forms of foraminifera appeared in Cambrian and since provide a long and well recorded evolutionary record throughout Paleozoic, Mesozoic and Cenozoic (BouDagher‐ Fadel, 2008). Based on life strategy, foraminifera are divided in two groups: benthic and planktonic foraminifera. Planktonic foraminifera passively float through the waters of open oceans moved by currents. Benthic foraminifera live on the sea floor; on the surface, buried into the sediment, or attached to plants, rocks or sediment particles. Based on their size and internal morphological structure benthic foraminifera can be divided into two groups; smaller and larger benthic foraminifera. The main criteria for identifying LBF is the complex internal structure which evolved to efficiently host photosymbionts, the key elements in the ecology of LBF. The symbiotic algae utilize the waste product of the foraminifera, allowing them to efficiently recycle of nutrients and to facilitate calcification (Ross, 1974; Leutenegger, 1984). This life strategy, LBF as a greenhouse, limits their occurrences to photic zone since algal symbionts are dependent on light for photosynthesis (Leutenegger, 1984). Besides light levels, the distribution and abundance of LBF is determined by relatively well‐known parameters, including hydrodynamic energy, water temperature, salinity, food availability and substrate type (Hottinger, 1983; Hohenegger, 1994; Renema, 2006). Therefore, the assemblage composition of fossil LBF can provide important and valuable data for paleoenvironmental reconstructions (Hallock and Glenn, 1986; Renema and Troelstra, 2001). 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 (Renema et al., 2008). Therefore, the data acquired from the fossil assemblages may contribute to our understanding of this biodiversity hotspot. In this thesis Miocene LBF were investigated in order to provide new insights regarding their biostratigraphy and depositional paleonvironments of Indonesia. The focus of the research includes mixed carbonate‐siliciclastic (MCS) systems of the Kutai Basin in East Kalimantan. However, to provide a comparative model with the blue‐water systems (Wilson, 2012), the study also included localities from Bulu Formation with carbonate platform deposits in Central Java. 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 (Friedman, 1988). However, recent studies reveal high biodiversity in these turbid water settings, including corals (Santodomingo et al., in press), LBF (Novak and Renema, in press), algae (Rosler et al., in press), and bryozoans (Di Martino and Taylor, 2014). The Kutai Basin was a host for the development of numerous MCS systems, with a peak of their deposition during the Miocene (Wilson and Rosen, 1998; Wilson, 2005). Herein MCS systems are defined as in situ mixing (Mount, 1984) with the carbonate fraction consisting of autochthonous or parautochthonous death assemblages of calcareous organisms accumulated on or within siliciclastic substrates. In these 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 in MCS systems (Lokier et al., 2009; Novak et al., 2013). By investigating LBF assemblages of Miocene MCS systems of the Kutai Basin by updating their biostratigraphy, providing environmental reconstructions, and comparing them with contemporaneous carbonate platform deposits, this research helps in untangling the origins of the Indo‐Pacific biodiversity hotspot.