9:45 AM - 10:00 AM
[BPT03-04] Calcareous nannofossil biostratigraphy in the Cikarang Member of the Jampang Formation at Ciletuh Palabuhanratu Geopark, Indonesia
Keywords:Calcareous Nannofossil, Biostratigraphy, Early Miocene, West Java of Indonesia, Ciletuh Palabuhanratu UNESCO Global Geopark
The reconstruction of biostratigraphy based on calcareous nannofossil in Ciletuh Palabuhanratu Unesco Global Geopark on Cenozoic sediments is still limited. This study aims to determine the age and present the new biostratigraphy records based on calcareous nannofossil of the Cikarang Member of the Jampang Formation from Ciletuh Palabuhanratu Unesco Global Geopark, Indonesia. The methods used to process the samples were smear slides was carried out by systematic sampling of rock samples and field data collection using the Measuring Stratigraphic Section method, with a total thickness of 30.4 m. Lithological characteristics at the bottom sediment rock sample are characterized by the appearance of non-carbonate sandstones, and the more the intersection of carbonate sandstones with claystone dominates until the younger section of samples. At least 19 genera and 68 species of calcareous nannofossils were identified, and several age-diagnostic species were detected. The biostratigraphic events recognised at the site consist of FCO Sphenolithus heteromorphus (17.721 Ma), LO Sphenolithus conicus (17.95 Ma), LCO Sphenolithus belemnos (17.973 Ma), FO Sphenolithus belemnos (18.921 Ma), FCO Helicosphaera carteri (21.985 Ma), FO Sphenolithus disbelemnos (22.413 Ma), FO Umbilicosphaera rotula (22.82 Ma), LO Ilselithia fusa (22.824 Ma), LO Cyclicargolithus abisectus (23.31 Ma), and LCO Sphenolithus ciperoensis (24.389 Ma). Based on the datum marker distribution, the age of the studied interval in the Cikarang Member of the Jampang Formation can be correlated with the Oligocene (NP 25) to the Early Miocene (NN4). A distinct feature of this area is the abundance and continuous occurrence of Sphenolithus spp., and the disappearance of Discoaster spp. throughout the studied interval. A reticulofenestrid coccolith, the Cyclicargolithus, dominates the distribution of nannofossil assemblages, constituting more than 50% of the abundance from younger to older age boundary samples. Significant changes in the ancient environment in this geopark are underscored by the abundance of Reticulofenestra spp. small size (constituting 75% of the total abundance). The results also show identification of warm-water taxa of coccolith from this study area, which have been dominated by Sphenolithus spp. were characterized by a relatively abundant productivity from 15% to 35% during the early Miocene. The early Miocene deposition of this formation may have occurred under oligotrophic conditions and warm seawater temperatures. The data record on the abundance of Sphenolithus and Cyclicargolithus coccolith at this study site can be used for further study. Otherwise, Nannofossil assemblage data records in paleoenvironment interpretation and geological age correlation with the other geological formations might be applied to the reconstruction of geological history and Cenozoic paleoclimate change records in Ciletuh Palabuhanrartu Unesco Global Geopark.