Some Considerations Concerning the So-called “Intraformational Fault” Developed in the Miura Group in the Miura Peninsula, Kanagawa Prefecture

Abstract

Different types of minor faults are well developed in the Neogene strata extensively distributed in the Miura Peninsula, Kanagawa Prefecture, Japan. In the Miura group, however, the development of minor faults is confined to its lower part, i. e., the Kamakura superformation.
Although the characters of a minor fault are generally different in various places, each minor fault may probably be originated in an unconsolidated or subconsolidated sediment. Minor fault of this kind is provisionally called “intraformational fault” by the writers.
In this paper, the characteristic features of the intraformational faults developed in the Kamakura superformation are described in detail, and the mechanisms of their origination are considered from the stratigraphical and sedimentological standpoints of view.
As to the mechanisms of origination of intraformational faults, different opinions have hitherto been expressed by some Japanese geologists. According to the writers' present opinion, the principal mechanisms of the intraformational faults in the Kamakura superformation are as follows :
1) Differential subsidence of sea-bottom which occurred during the deposition of strata.
2) Submarine sliding which occurred during the deposition of strata.
3) Differential compaction of strata caused by the lateral changes in rock-facies as well as in thickness of strata.