F. Masuda, ONLAP AND DOWNLAP PATTERNS IN PLIO PLEISTOCENE FORE-ARC AND BACKARC BASIN-FILL SUCCESSIONS, JAPAN, Sedimentary geology, 93(3-4), 1994, pp. 237-246
Discontinuities such as onlap, toplap and downlap terminations, are im
portant key structures in seismic stratigraphy. These patterns charact
erize the Plio-Pleistocene Kakegawa Group in Shizuoka, the middle Plei
stocene Kasamori Formation in Chiba, and the Plio-Pleistocene Uonuma G
roup in Niigata. The patterns within these successions can be detected
by tracing intercalated pyroclastic layers (tephra beds), which provi
de the same information as the synchronous reflection lines in seismic
data. These pattems, therefore, allow the stratigraphic sequence to b
e divided into forearc and backarc basin-fill successions. The deposit
ional sequences of the Kakegawa and Uonuma groups are third-order, ran
ging from ca. 2.6 Ma to 1.0 Ma. The Kasamori Formation has high-freque
ncy sequences dating from 0.60 Ma to 0.45 Ma. All these sequences are
believed to have been produced by glacio-eustatic sea-level changes.