Studies of the recent foraminifera of the Sunda Shelf and the Java Sea

Abstract

Five foraminiferal assemblages based on benthonic foraminifera are established on the wide Sunda Shelf and the java Sea. The inner shelf (18-2 fm) assemblage is represented by Amphistegina radiata (Fichtel and Moll), Calcarina spengleri (Gmelin), Elphidium crispum (Linné), Operculina ammonoides (Gronovius), and Quinqueloculina seminula (Linné). The central shelf (27-3 fm) assemblage is represented by Quinqueloculine-Rotalia spp., Asterorotalia trispinosa (Thalman), and Elphidium craticulatum (Fichtel & Moll). The outer shelf (36-42 fm) is represented by BolivinaBulimina-Uvigerina spp., cancris auriculus (Fichtel & Moll), Quinqueloculina cf. akneriana d'Orbigny and Rolshausenia rolshauseni (Cushman & Bermundez). The shelf edge (97 fm) assemblage is poorly defined. The lower middle bathyal (832 fm) assemblage is represented by Bolivina-Uvigerina spp., Cassidulina subglobosa Brady and Cibicides tapoengensis LeRoy. Five zones developed by using faunal breaks of planktonic foraminifera could be correlated with the benthonic foraminiferal assemblages. The shelf is dominated by shallow-water benthonic foraminiferal species, while the planktonic foraminifera dominate the lower middle bathyal area. High species diversity are found to correlate with possible relict assemblages at a time of lower sea-level. Relict distributions of Elphidium spp. and Rotalia beccarii indicate a possible stillstand of sea-level at 37-42 fm. Core V19-135 was chosen for detailed studies of possible sea-level fluctuations. Three possible explanations are proposed based on the limited data, and the eustatic change of sea-level seems to provide the best explanation of the results.