STRATIGRAPHY, PALEONTOLOGY AND DEPOSITIONAL SETTING OF THE UPPER EOCENE (PRIABONIAN) PAGAT MEMBER, TANJUNG FORMATION IN THE SATUI AREA, ASEM ASEM BASIN, SOUTH KALIMANTAN, INDONESIA

Marine sedimentary rocks of the Upper Eocene Pagat Member of the Tanjung Formation in the Asem Asem Basin near Satui, Kalimantan (Indonesian Borneo), provide an important geological archive for understanding the paleontological evolution of southern Kalimantan in the interval leading up the development of the Central Indo-Pacific marine biodiversity hotspot. In this paper we describe a moderately diverse assemblage of marine invertebrates within a sedimentological and stratigraphical context. The Pagat Member records an interval of overall marine transgression and chronicles a transition from the marginal marine and continental siliciclastic succession in the underlying Tambak Member to the carbonate platform succession in the overlying Berai Formation.

The lower part of the study interval comprises heterolithic interbedded siliciclastic sandstone and glauconitic shale. This segues into a calcareous shale succession with common foraminiferal packstone /rudstone lenses interpreted as low-relief biostromes. A diverse trace fossil assemblage, which occurs primarily in the muddy / glauconitic sandstone and bioclastic packstone / rudstone lithofacies, constrains the depositional setting to a mid-ramp / mid to distal continental shelf settings below fairweather, but above storm wave base.

Each biostrome rests upon a storm-generated ravinement surface characterized by a low-diversity Glossifungites or Trypanites trace fossil assemblage. The erosional surfaces were colonized by organisms which preferred stable substrates including Larger Benthic Foraminifera, solitary corals, oysters and serpulids.

The biostromes comprised loci of exceptional marine biodiversity on the muddy Pagat coastline, containing 14 genera of Larger Benthic Foraminifera, ~30 mollusc taxa, at least five brachyuran decapod genera, six coral genera (Cycloseris, Trachyphyllia, Anthemiphyllia, Balanophyllia, Caryophyllia, and Trochocyathus), as well as a variety of bryozoans, serpulids, echinoids, and asterozoans. High foraminiferal and molluscan diversity, coupled with modest coral diversity, supports the hypothesis that the diverse tropical faunas that characterize the Coral Triangle were initiated in the latest Eocene /earliest Oligocene.