Molluscan fauna of the lower Gelingseh Beds s. str., Sangkulirang area, Kalimantan Timur (East Borneo)

A compilation is given of the results of an investigation of all the molluscs collected by L.M.R. Rutten some seventy years ago, at five localities in the type area of the Gelingseh Beds s. str., Late Miocene. Thirteen new species are described, viz, Smaragdia gelingsehensis, Rissoina maduparensis, Architectonica ickeae, Strombus ickeae, Hexaplex sampajauensis, Hinia gelingsehensis, Olivancillaria altenai, Melo persolida, Gibberulina menkrawitensis, Strioterebrum gelingsehense, Ringicula seriaensis, Spondylus apiapiensis, and Linga antjamensis. For over fifty years the Gelingseh Beds have been correlated with the Upper Balikpapan Layers, Tf3 (Preangerian). According to Rutten's field work, the fossil localities occur at approximately the same level in the lower part of the Gelingseh Beds. However, now, as before (concluded by K. Martin), it seems that the fauna from the 'Source area of Sungai Gelingseh' (presently dubbed A) could be a little older than the fossil assemblage obtained at a locality known as just 'Sungai Gelingseh' (B-Bb in the present paper), and to correlate with, say, the apparent overlap in time of type Rembangian on to Preangerian. Loc. B-Bb yielded the largest fauna, which offers ample evidence of a full-blown Preangerian status, and so does fauna C (from Rutten's loc. 144). On the other hand, faunas D (loc. 149) and E (loc. 150) jointly seemingly represent a higher stratigraphic level of Tf3 - with a possibility that Odengian is approached, if not actually reached - to date however there being known no Bornean faunas of a comparable composition and age. As to the relationships with other Preangerian faunas of Borneo, Java and Sumatra, the Gelingseh faunas invariably show strong ties with the assemblage of the basal Menkrawit Beds of nearby Mangkalihat Peninsula (L. 114, Leupold) and also, and sometimes even more strongly so (faunas Bb and C), with the classical Javanese Preangerian, except however faunas A and B. Among themselves, faunas A to E show relationships varying as much in quality as their several ties with Preangerian faunas both distant and near.