Extract

In the northern Arabian Sea the Arabian, Eurasian and Indian Plates are in tectonic interaction with one another. We present interpretations of multichannel seismic profiles across the Makran subduction zone (which is part of the Eurasian-Arabian Plate boundary) and the transtensional Murray Ridge and Dalrymple Trough (which are part of the Arabian-Indian Plate boundary). We distinguish four megasequences in the sedimentary succession, which we correlate over the entire study area. Regional unconformities separate the megasequences and enable us to establish a common history of the region before Late Miocene time (c. 20 Ma). The Early Pliocene (c. 4.5 Ma) reopening of the Gulf of Aden caused a reorganization of the plates and subsequent tilting of the oceanic crust of the Arabian Plate toward the Makran subduction zone. This event is documented by the regional M-unconformity. Since that time, sedimentation on the Oman Abyssal Plain has been permanently separated from the Indus Fan by the Murray Ridge, on the northern end of which there has been no significant sedimentation.

The northern Arabian Sea can be divided into four units, on the basis of physiographic and structural characteristics: (1) the Makran Accretionary Wedge; (2) the Oman Abyssal Plain; (3) the Murray Ridge system; (4) the Indus Fan (Fig. 1). The units meet at the triple junction of the Eurasian, Arabian and Indian Plates west of Karachi.

The Makran Accretionary Wedge extends some 1000 km from Iran to central Pakistan. Its topography ranges from more than 3000 m below sea level to heights