THE ARCHITECTURE AND PROVENANCE OF A GIANT MASS-TRANSPORT DEPOSIT IN THE ARABIAN SEA: THE NATARAJA SLIDE

The Nataraja Slide was recently discovered by seismic mapping off the west coast of India in the Arabian Sea. Volumetrically estimated to be ~19,000 km³, it is the second largest mass-transport deposit known on a passive margin. Understanding how this deposit was emplaced is important to constrain how mass wasting affects the bathymetry of sedimentary basins and effects, such as tsunamis generated by such events. The Nataraja Slide was emplaced ~10.8 Ma as a result of collapse of the western Indian margin running 550 km into the basin. The deposit has been cored in two locations by the International Ocean Discovery Program (IODP) Expedition 355 in places where it is ~330 m (Site U1456) and ~190 m thick (Site U1457). The presence of various deformation structures and the beginning of reworked microfossil assemblages is used to define the top of the deposit. The deposit appears to have two units at Site U1456, suggesting emplacement in two large pulses. Each unit has a coarse carbonate-dominated base, composed of clast-supported and matrix-supported breccia interpreted as debris flows. Within these breccias, coherent carbonate blocks from the Indian continental margin are present and are overlain by massive calcarenite associated with high-energy current transport, and calcilutite. These strata are overlain by steeply inclined, slumped but otherwise coherent pyritized, siliciclastic mudstones with minor amounts of siltstone, interpreted as turbidity currents. Emplacement appears to have eroded significant thicknesses of Indus Fan turbidites at Site U1456, as there is a hiatus spanning ~5 m.y. at the base. At Site U1457, the slide directly overlies Paleocene reddish mudstones on the eastern flank of the Laxmi Ridge, whose presence diverted the deposit to the south in the Laxmi Basin and away from the main Arabian Sea basin. Bulk sediment Nd and Sr isotope geochemistry show a provenance, similar to those of the Tapti and Narmada rivers in western India, but leave open entrainment of Indus Fan turbidites in the slump top and drape. Our study aims to further evaluate the depositional mechanisms and original trigger for the mass wasting by using basic petrography and core descriptions to understand the sediment in this late Miocene mass-transport deposit.