The continental margin along the northern boundary of the study area differs 

 in several respects from the eastern margin . In general, the topography is more 

 irregular. Off western Pakistan, the continental shelf is usually less than 20 miles 

 wide and narrows to an average width of less than 10 miles off the Iranian coast . 

 The shelf breaks at about 70 fathoms. The continental slope is often broken by a 

 small marginal plateau or terrace at depths in the vicinity of 700 to 900 fathoms. 

 The marginal plateau or terrace ranges in width from about 10 to 35 miles, and the 

 degree or extent of development of this feature varies widely. 



The shelf at the head of the Gulf of Oman is again quite broad . The depth of 

 the Strait of Hormuz is about 40 fathoms . Between the head of the Gulf and Ra's 

 Al Hadd, the continental shelf gradually narrows, reaching a minimum width of 

 about a mile. At several points between Masqat and Ra's Al Hadd, the shelf is 

 virtually absent. The continental slope here is quite steep. South of Ra's Al Hadd, 

 the shelf again broadens, the topography becomes generally smoother, and a conti- 

 nental rise is well-developed . 



The deep-sea floor of the northern Arabian Sec consists of two separate and 

 reasonably distinct basins separated by the northeast-southwest trending Murray 

 Ridge. The Arabian Sea Basin, which is located southeast of the Murray Ridge, Is 

 completely dominated by the Indus abyssal cone, a huge mass of sediment ultimately 

 derived from the Indus River. In general it is a smooth feature broken only by a 

 complex system of turbidity current distributaria . Heezen and Tharp (1964) note the 

 presence of large natural levees on the Indus cone^ constructed to heights of over 

 400 fathoms . The area northwest of the Murray Ridge comprises the Gulf of Oman 

 Basin . Heezen and Tharp (1965 a, b) show two relatively small abyssal plains in 

 this portion of the study area . The larger of the two is called the Oman Abyssal 

 Plain and occupies the central floor of the Gulf. Another long narrow plain extends 

 southward from the Oman plain between the continental rise and the Murray Ridge. 



The Murray Ridge consists of a linear series of seamounts, scarps, and small 

 basins which exhibit maximum reliefs ranging from 800 to 1,500 fathoms. Lineation 

 of some of the scarps, particularly at the northern end of this feature, strongly sug- 

 gest fault origin . The deepest spot in the study area is slightly over 2,300 fathoms 

 and is a depression in the ridge line to the southwest. The tops of the various topo- 

 graphic highs making up the ridge (some of which are flat) range between 200 and 

 500 fathoms in depth . 



13 



