Abstract
In view of that continental shelves are essentially the erosional landform and also that the sea level fluctuation after Wurm glacial stage has played an important role i n the for mation of continental shelves, the author completed a model of continental shelf formation, which was based on a combination of coastal cliff recession and the postglacial transgression; the model is summarized in the following two equations:
_??_ (1)
and Z*=-ha+A(1-2e-at+e-2at), (2)
where X* and Z* are the coordinates showing the position of the point P (Fig. 9) and a continental shelf profile may be obtained by finding a locus of this point; c is the recession rate of the present coastal cliff, in meters per year; t is time in years, and t=0 and t=2×104 show 2×104 years B. P. and the present respectively; ha is the critical water depth for submarine bedrock erosion, in meters and may be estimated approximately by
_??_
in which H0 and L0 are the deep water wave height and length in meters respectively and H and L are the wave height and length in meters, at the water depth ha respectively, and a nomogram for this equation is shown in Fig. 1; W0 is the width of abrasion platform in meters at t=0 and is written as
W0=Wp-2×104c,
in which Wp is the present platform width, defined as the horizontal distance from the present coastline to the place where water depth is ha; A and a are constants appeared in the following equation expressing the curve of the postglacial sea level change:
Z=A(1-2e-at+e-2at)
which is shown in Fig. 8 and A=125 and a=1.98×104 in this case.
The validity of this model was examined in three areas facing on the Pacific Ocean (Fig. 10). Physiographical and oceanographical conditions of these areas are listed in Table 2. Figure 15 shows comparisons between the continental shelf profiles in the fields and the ones calculated by using Eqs. (1) and (2); the actual profiles and the calculated ones are in fairly good agreement: this model can explain in full degree the first essentials of continental shelf formation.
