Large benthic foraminifera from the deep photic zone of a mixed siliciclastic-carbonate shelf off East Kalimantan, Indonesia

Abstract

Living large benthic foraminifera (LBF) were analyzed from three transects of boxcores taken on a shelf off the coast of East Kalimantan, just north of the Mankalihat Peninsula. The transects were located at different distances to the mouth of the Berau river. In 45 boxcores, of which 28 contained living LBF, 20 species were recognised. They occurred in moderate to high density outside the pro-delta, i.e., outside the area with high clay and silt sedimentation. LBF characteristic of sandy substrates can be divided into two or possibly three assemblages, shallow (15–50 m), deep (50–85 m) and possibly very deep (> 85 m). The latter is poorly developed in the study area. Few LBF were recorded in one of the three transects, possibly because of either sediment instability or physical or chemical parameters of the sediment. Grain-size analysis of samples in the other transects indicates that LBF occurrence strongly modify the habitat. After colonisation, grain-size increases, creating more opportunities for other species and higher densities of LBF.