SYMPOSIUM ON SEDIMENTATION AND 



CHARACTERISTICS OF SEA BOTTOM 



IN THE PACIFIC BASIN 



SEDIMENT DISTRIBUTION ON THE EAST ASIATIC 

 CONTINENTAL SHELVES(^) 



By Francis P. Shepard, Scripps Institution of Oceanography, 

 University of California 



[.4 hstract] 



During the war charts were prepared for the United States Navy 

 showing the bottom character on the continental shelves along the 

 eastern and south-eastern coasts of Asia. They are based on about 

 four hundred thousand bottom notations ' from the most detailed 

 Japanese, British, Dutch, and French charts which were available in the 

 files of the Nav}^ Hydrographic Office. The final charts were printed in 

 small numbers by the Hydrographic Ofhce. 



The charts show that sediment is distributed irregularly over the 

 Asiatic continental shelves. In few places is there a graduation outward 

 from coarse sediment to fine. Along much of the Asiatic coast mud 

 predominates on the inner shelf, and sand outside. Large rock areas 

 occur, particularly along the Japanese coast where the Kuroshio 

 (Japanese Current) is flowing at a high speed. Rock notations are 

 abundant on submerged hills, off rocky points, in narrow straits, and at 

 the outer edge of the shelves. Mud is found in enclosed bays, and sand 

 is most common in broad open bays, although mud is present in the 

 latter off some large rivers. Sand is the most common type of sediment 

 reported from the Asiatic shelf. The distribution of the sediments is 

 controlled by such factors as (1) sources (large rivers, shore erosion, 

 organic growth, and recent vulcanism), (2) currents (oceanic, tidal, and 

 longshore), (3) waves (on exposed points), (4) bottom topography 

 {submerged hills, basins, and canyons). 



Summary of Discussion 



Dr. Shepard's results had tended to show that rock notations were 

 encountered most commonly in straits and areas subject to great current 

 sweep, sand on beaches with no large rivers entering, and on continental 

 shelves, and mud in river deposits, inner parts of shelves, and at the 

 heads of submarine canyons. 



Mr. Powell, speaking of the results of a ten to fifteen years bottom 

 survey of the Waitemata Harbour and Hauraki Gulf, was able to point to 

 results exactly similar to the conclusions of Dr. Shepard. Coarse sedi- 

 ments were found in the middle of the Auckland Harbour along the tidal 

 current, and fine sediments from soft Tertiary mudstones at the sides. 

 But in the case of the outer islands the normal distribution described in 

 such localities by Dr. Shepard was likewise adhered to. Heavier material 

 is tossed inshore, mud occurring in the deeper portions. It was pointed 

 out b}' Mr. Powell that the hard bottom sediments in his area were purely 



(1) Shepard, F. P. ; Emery, K. O. ; and Gould, H. R. (1949) : Allan Hancock 

 Foundation Publications, Occ. Pap., No. 9, pp. 1-64. 



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