The lowstand systems tract of the standard sequence-stratigraphic model consists of three major component units—in ascending order, the basin-floor fan, slope fan, and lowstand wedge. However, there are no modern or ancient examples of a lowstand systems tract that contain each of the three component units from the base to top. Three-dimensional outcrop analysis and detailed chronostratigraphic correlation of the lowstand deposits that infilled the Pleistocene Kazusa forearc basin exposed on the Boso Peninsula of Japan reveal that the three component units of the lowstand systems tract are largely age equivalent. Their development was controlled much more by geographic setting, in conjunction with spatial variation in sediment supply and basin subsidence, than by the position of relative sea level. It is concluded that the lowstand systems tract of the sequence-stratigraphic model is a theoretical concept that is not accurately reflected in the stratigraphic relationships shown in the present field case.

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