The Miocene (25.2 – 5.6 million years ago) climate changes recorded by foraminifera and nannofossils assemblages in Bogor Basin, Western Java

Abstract

The Miocene composite sections reveal that a bathyal to the inner neritic setting (20 - 500 m sea level depth) was being filled dominantly by fine siliciclastic, which deposited in fluctuate of warm to a temperate climate. The quantitative data of total abundancy, species number, marker species ratio, shell coiling direction ratio and size guided to sea surface temperature realms. The warm zone was determined based on high total abundance and diversity, a high frequency of foraminifera and nannofossil tropical marker species, dominated by dextral coiling direction, and relatively big size-specific foraminifera taxa. On the contrary, warm temperate zones were identified by lower total abundance and diversity. In the lower part, the sediments contain medium to high -abundance and -diversity of foraminifera as well as nannofossil assemblages indicated a warm climate at the Earliest Miocene (25.2-24 Ma). The low -total abundancy and -species number that indicates a decrease in temperature were recorded until the earliest Middle Miocene (24-20 Ma). The dominance of Orbulina group with a high frequency of tropical species marker (Globoquadrina altispira, G. globosa, Globigerinoides trilobus, G. sacculiferus and Discoaster group) indicated significant increase in temperature. The optimum of total- and individual- abundance along with the dominated of big size-Orbulina, increased tropical foraminifera, and nannofossil species markers indicate a warm climate at Middle Miocene (16-13.8 Ma). The decreased dextral relative shell coiling ratio of Globorotalia menardii and Globorotalia acostaensis, abundance and diversity of assemblages or taxa markers that indicate the temperature decrease is recorded in Late Miocene interval several times. An increased number of Calcidiscus leptoporus, Coccolithus pelagicus, Discoaster challengeri, D. variabilis, and Hayaster perplexus, the less -total abundance and -diversity indicated a warm temperate climate (10 to 6.2 Ma). It is considered to correlate with the global glaciation period.