This research was conducted to observed the paleoecological condition of the Tapak formation. This formation had been predicted to change on its paleobathymetry. The change of paleobathymetry can affect the paleoecology. The paleoecological dynamic was observed by the abundance and paleodiversity of both nannofossils and benthic foraminiferas. It tended to decline from old sample to the younger. The relative age was analyzed using nannofossil biozone which showed an end of the initial Pliocene sample, i.e., NN14 to no younger than NN15 (4.2 million years ago lower than 3.5 million years ago). The depositional environment and paleobathymetry were analyzed using the indicator species of foraminiferas. Changes in paleoproductivity were observed for the basis of primary productivity, which the older sample was higher than the younger. The content of TOC (Total Organic Carbon) in the older sample was higher than the younger. In general, this sample was relatively less potential as a source rock due to the low production of TOC. The content of CaCO₃ relatively increased in the whole sample, but in the A21N sample, the content of CaCO₃ raised significantly. Ancient oxygen condition analyzed with indicator species of benthic foraminiferas revealed a similar trend to the secondary productivity. CCA of nannofossils showed three groups of environmental variables, whereas CCA of foraminiferas resulted in two groups.

Bayu Awifan Dwijaya

Romanus Edy Prabowo

Gentur Waluyo