Bottom Sediments in Bays of North Kyushu

Mitsushio Hiromi

doi:10.5109/1543653

The present paper contains the result of distributional and textural analyses of bottom sediments in several selected bays of North Kyushu which represent varying degrees of embayment from closed to opened one. Generally mud content in sediments is related with the embayment degree of bays; a bay with higher degree of embayment has more muddy sediments. Four sedimentary environments in relation to textural composition of bottom sediments are recognized: (1) bay-mouth environment with sandy sediments, (2) bay-centre environment with muddy ones in closed bays and with sandy ones in opened bays, (3) bay-head environment with muddy ones, and (4) coastal environment with gravelly ones and rocky bottom. Textural composition of the sediments shows that the best sorting is within the medium-sand grade, both below and above this size grade the sorting becoming poorer, and that the maximum coarse skewness occurs in the grades of very coarse and fine sands whereas the minimum one in those of medium sand and coarse silt. This feature agrees well with the result of study of recent fluvial sediments by FOLK et al. (1957) and that of modern deep-sea sediments by HUBERT (1962) among others. It seems to be significant that the textural characteristics of the present sediments are similar both to those of fluvial sediments and to those of bathyal ones, even if they are recent or ancient.

Bottom Sediments in Bays of North Kyushu

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