| 概要 |
The purpose of this study is to clarify the sedimentary environments and the nature of recent sediments. This study is now in progress, and the results are preliminarily outlined on this occasion. The... sea around the Tomioka peninsula may be divided into 4 sea-areas on the basis of physiography and submarine topography. 1. "A" sea-area is the Tomoe cove called Tomoe-ura defined by the recurved spit. 2. "B" sea-area is the Tomioka bight which is characterized by shoaling beach and submarine drain related to the paleo-Shiki river. 3. "C" sea-area is the northern part of the Tomioka peninsula and bight. The eastern part of it is characterized by a relief and a small hollow. The western part of it is characterized by a monotonous slope. 4. "D" sea-area is the southwestern part of the peninsula, characterized by more gentle slope. In 1960, 38 bottom sediment specimens were dredged and collected. Their stations are shown in Figure 2. 3 specimens of them are gravels, and treated with measuring of statistic method. 1 specimen of them is muddy sediment, and is treated with pipette method. The rest 34 specimens are sandy sediments, and are treated with sieving method. Based on the results of mechanical grain analysis, 4 types are distinguished in the bottom sediments of this surveyed area. These types are described briefly below: Type I is represented by muddy sediment. This type distributes in "A" sea-area or Tomoe cove. It is well-sorted. Type II is represented by medium sand. This type distributes mainly in the western part (" D" sea-area) and. partly northeastern part (" B" sea-area) of Tomioka bight. Itis wellsorted. Type III is represented by coarse sand and shell sand. This type distributes mainly in the northern part (" C" sea-area) of Tomioka. This is coarser and worse in sorting than the sand of type II. Type IV is represented by small pebble or granule. This type distributes mainly in the northern part (" C" sea-area) of Tomioka. This type is also found in a small area of the "D" sea-area. This is the coarsest sediment in the surveyed area. The larger pebbles than in type IV are dredged from Stations 17, 54 and 59. Many benthonic animals are found on these pebbles. Rocky basement occurs in the western part of Tomioka (mainly "C" sea-area), but could not be dredged. These sediments are not concerned with the depth. But they have a close relation with the sea-area or their depositional environments. Benthonic animals, for instance brachyurans, sea weeds and shellfishes, have close relations with the sea-areas defined herein and the types of bottom sediments.続きを見る
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