New Ichthyoliths from Ferromanganese Crusts and Nodules from the Central Indian Ocean Basin

Abstract

Ferromanganese encrusted hardgrounds, their intraclasts and the nuclei of manganese nodules collected from the central Indian Ocean basin have yielded plentiful numbers of ichthyoliths. Forty well-known ichthyoliths, one new type and 35 new subtypes are encountered. To accommodate these newly recovered ichthyoliths, the coded descriptive system for the taxonomy of ichthyoliths (Doyle and Riedel 1979a and its later modifications) is updated herein. New ichthyoliths are described and illustrated. A majority of them are believed to be of Paleogene age. INTRODUCTION SYSTEMATICS The distribution of microscopic skeletal fragments of fishes or ichthyoliths has been studied in various DSDP sites from the world's oceans. Recent works of Edgerton et al. (1977), Kaneps et al. (1981), Doyle and Riedel (1979b, 1985a and 1985b), Gottfried et al. (1985) and Tway et al. (1985) have established biostratigraphic ranges of the ichthyolith subtypes, which can be used for correlation in otherwise unfossiliferous pelagic Tertiary sediments. The ferromanganese encrustations and the nodules collected during various cruises for the survey of polymetallic nodules in the central Indian Ocean basin (text-fig. 1, table 1) yielded many ichthyoliths in otherwise unfossiliferous substrates and nuclei of encrustations and nodules. The nuclei and substrates of ferromanganese nodules and encrustations are made up of burrowed and bored pelagic clays. The earlier described ichthyoliths are recognized and many new ichthyoliths are encountered. In this paper, the author has attempted to describe new ichthyoliths by modifying the coded descriptive system of ichthyoliths. MATERIAL AND METHODS The nuclei and substrates of the ferromanganese encrustations and nodules are chiefly of two types; altered basalts and pelagic claystones and clayclasts. Tie clayclasts are the intraclasts of burrowed and bored pelagic hardgrounds (Gupta, in prep.). The nuclei material was scraped with a sharp knife and broken into small pieces (0.5cm), dried, weighed and dispersed in sodium hexa-meta-phosphate then boiled in H202 for 4 hours. The material was sieved on a 62gm mesh screen. The fragmentary fish micro-remains were picked using a fine camel hair brush under a binocular microscope, placed on glass slides and then mounted in Canada balsam. These fish micro-remains were studied under a transmitted light microscope and identified by decoding the coded descriptors. The type material and subtypes of the newly described ichthyoliths are housed at the Geological Oceanography Division of the National Institute of Oceanography, Dona Paula, Goa 403 004, India. The taxonomy of ichthyoliths is determined by decoding the coded descriptive system given by Doyle et al. (1974), Dunsworth et al. (1975), Ramsey et al. (1976), Doyle and Riedel (1979a, 1980, 1985b), Gottfried et al. (1984), Tway et al. (1985) and Winfrey et al. (1987) and are described using the same 70' E 80' IO N \\I LEiAi890 I