Introduction

R/V Pelagia Cruise SME 117 INDUS

INTRODUCTION	Pelagia in Mutrah, Oman

The Indus River is the great river of the western Indian subcontinent and flows from Mount Kailas in western Tibet until it meets the Arabian Sea, just to the east of the city of Karachi, Pakistan. In this place it forms the 5th largest delta in the world, and feeds the world's 2nd largest sediment body, the Indus Fan.� This is more than four million cubic kilometers of sediment eroded from the Himalaya and which lies under the shelf and continental slope of Pakistan and western India.
It stretches far into the abyssal depths of the northern Arabian Sea, stretching ~1500 km towards the Carlsberg Ridge. How did this body form and what does this tell us about mountains building and past climate change? Although the outer shelf had previously been surveyed for shallow-penetrating seismic and bathymetry by a team from the German geological survey (BGR), the character of the inner shelf has not be imaged beyond basic plumb line soundings in the 19th and mid 20th centuries. Onshore some knowledge of the Indus delta exists as a result of shallow coring of Holocene sediments, most recently during a US funded campaign of coring in 2003-2004 near the modern mouth of the Indus River. Workers discovered that the delta coast moved oceanwards even during the Early Holocene (11,000-8,000 yrs ago). This is surprising because this was a period of rapid sea level rise after melting of the glaciers of the last ice age. This delta progradation implied very rapid rise in sediment supply rate at that time driven by strong monsoon rains. The purpose of this cruise is to map the previously undocumented inner continental shelf of Pakistan in order understand how sediment moves from the river to the deep sea Indus submarine fan. Earlier coring had established the fact that sediment delivery to the fan has ceased by 11,000 years ago. Although the prograding Indus delta has clearly not reconnected with its deep sea fan it had been shown that sedimentation rates were at a maximum between the head of the canyon and the mouth of the river, despite the sharp drop in sediment supply because of damming in the late 20th century. Our objective is to understand how sediment is moved from the river mouth to the canyon and how this has changed since the end of the last ice age (~20,000 yr ago). Our work is important for general Earth science research in understanding how deltas forms and how the land responded to a period of strong global warming. However, the project is also of interest to the oil and gas industry who search for hydrocarbons in sands in ancient, as well as modern deltas. In order to accomplish these goals we have a programme of seismic surveying and coring of the inner shelf.