@conference {2017, title = {Microbial carbonates in Miocene reefs in the Mahakam Delta in East Kalimantan, Borneo, Indonesia}, booktitle = {SAGE2013 - Southeast Asian Gateway Evolution}, year = {2013}, month = {11/03/2013}, address = {Berlin, Germany}, abstract = {

Microbial carbonates are deposits that form by the activity of bentic microbial communities. Microbialites usually form domical, columnar or conical structures and can have laminated, clotted, dendritic or homogenous macrofabric. They have a broad distribution and can grow in a variety of different environments such as hot springs, freshwater lakes, hypersaline lakes, reefs and other marine environments. This research focuses on microbialites associated to coral reefs. Coral patch reefs in the Miocene Mahakam Delta in East Kalimantan (Borneo, Indonesia) grew in shallow marine turbid waters. These patch reefs developed from delta front to deeper (prodelta) settings in areas with temporary reduced siliciclastic input. Langhian reef deposits are well exposed in limestone quarries in the Samarinda area and locally include microbial carbonates. Two different types of microbial carbonates have been found around Samarinda in two localities 2 km apart. These sections were logged in detail and 208 samples were collected. Meso and macrostructure of microbialites were identified at the outcrops. Thin sections from carbonate samples were examined under optical microscope and microfacies were classified using the Dunham (1962) and Embry and Klovan (1971) terms. The carbonate content was analyzed using Total Inorganic Carbon analysis, with 12\% carbon as a standard for carbon calibration. In the northern section, microbialites occur as low-relief domes, up to 2 m wide and 0.5 m high, with internal lamination, developed around large coral fragments at the transition from reef deposits to fine-grained siliciclastics.
The second type of microbialites has been found in the southern locality as decimeter-scale nodules (\"megaoncoids\") formed around nuclei of large coral fragments. Small nodules were bound together into bigger nodules. Microbial micrite with laminated to digitated fabrics intergrew with coralline algae to form the thick covers of these \"megaoncoids\", which laterally change into coral boundstones. In both sections microbialites are not components of the reef framework. They grew around large coral fragments on the flanks of the patch reefs. The microbialites that form low relief domes developed on a nearly flat, stable seafloor seawards of the patch reef. The \"megaoncoids\" in the southern section formed as a result of downslope movement of coral fragments coated by microbialite/coralline algal crust. The steep slope at the flank of the patch reef favoured falling and overturning of encrusted corals and continued growth of microbial crusts on other sides of nodules.

}, author = {Vedrana Pretkovi{\'c} and Juan C. Braga and Vibor Novak and Anja R{\"o}sler and Willem Renema} } @article {2007, title = {Environmental reconstruction of a late Burdigalian (Miocene) patch reef in deltaic deposits (East Kalimantan, Indonesia)}, journal = {Palaeogeography, Palaeoclimatology, Palaeoecology}, volume = {374}, year = {2013}, pages = {110-122}, abstract = {

Most studies of Cenozoic shallow-water, mixed carbonate-siliciclastic depositional systems have focused on their sedimentology. To date, however, comprehensive analyses of biotas and biofacies of Indo-West Pacific reefs that developed in mixed carbonate-siliciclastic systems are lacking. This study describes the palaeoenvironment and biodiversity of a late Burdigalian patch reef that developed in a mixed carbonate-siliciclastic depositional system. The studied exposure is located at the northeast margin of the Kutai Basin near Bontang (Indonesia), and is approximately 80 m wide and 25 m thick. Multi-taxon analysis of the most abundant fossil groups, including larger benthic foraminifera, corals, coralline algae, and bryozoans, aims to provide a model for environmental interpretation that will allow comparison with similar deposits of Indo-West Pacific region. Based on fossil content and lithology, five different facies types have been distinguished: foraminiferal packstone (FP), bioclastic packstone with foralgal communities (BP), thin-platy coral sheetstone (CS), platy-tabular coral platestone (CP), and shales (S). Among larger benthic foraminifera, smaller and more robust forms dominate in the FP and BP facies, while larger and flatter forms are the most abundant in the CS and CP facies. Thin-platy corals are dominant in the CS facies and gradually change into thicker platy-tabular forms in the CP facies. Assemblages and growth forms of coralline algae show no major differences between the facies types and are dominated by melobesioids and Sporolithon. The majority of bryozoan species are encrusting and were found only in the CS facies. Light-dependent organisms occurring in the reef indicate low light conditions typical for mesophotic reefs. The relatively small size of this reef complex and quite distinct vertical changes in the facies types, combined with the high siliciclastic content in most of the units, points to strong terrigenous input affecting water transparency as the main factor controlling the reef growth.

}, doi = {http://dx.doi.org/10.1016/j.palaeo.2013.01.009}, author = {Vibor Novak and Nadiezhda Santodomingo and Anja R{\"o}sler and Emanuela Di Martino and Juan Carlos Braga and Paul D Taylor and Kenneth G. Johnson and Willem Renema} } @conference {2006, title = {Foraminiferal assemblages in Miocene carbonates of Indonesia}, booktitle = {Southeast Asian Gateway Evolution: SAGE2013}, year = {2013}, month = {11/03/2013}, address = {Museum fuer Naturkunde, Berlin}, abstract = {Neogene carbonates in Indonesia are characterised by different depositional environments. We studied localities outcropping on Mangkalihat Peninsula, Kutai Basin, and Java, that were deposited in a time interval from Early (Te5) to Middle Miocene (Tf2). In order to reconstruct depositional environments and obtain biostratigraphic information, larger benthic foraminifera (LBF) assemblages were analysed from these three locations. The northernmost, and stratigraphically oldest, from the studied carbonates are exposed on Mangkalihat Peninsula. They were formed in shallow-water environment on carbonate platform. Stratigraphically important LBF indicate Early to Middle Miocene age (Te5-Tf1). Towards the south, in the Kutai Basin, isolated patch reefs occur within siliciclastic sediments, developed in mixed carbonate-siliciclastic depositional systems. In general, LBF assemblage is indicative of low-light conditions typical for mesophotic reefs. Based on LBF late Early to Middle Miocene age (Tf1-Tf2) can be suggested. The southernmost carbonate exposures are located on Central Java, in the Bulu Limestone member. The LBF assemblage composition indicate environmental conditions typical for continental shelf edge. Middle Miocene (Tf2) can be inferred for these limestones based on LBF. Here we present an overview of Indonesian Early to Middle Miocene LBF assemblages in a range of depositional environments. We will assess the interplay between stratigraphical and environmental control on LBF assemblages. }, author = {Vibor Novak and Willem Renema} }