Visualization of the Internal Structure of the Massive Division in Experimental Sediment-Gravity-Flow Deposits by Mapping of Grain Fabric

A method for mapping of grain fabric is proposed for analysis of the cryptic internal structure of massive sedimentary units. The method is applied to the analysis of an experimental debris-flow deposit, revealing a number of characteristic features of this type of mass sedimentation. The debris flow was simulated in the laboratory using a channel inclined 30° opening onto a 10° slope, and transverse thin sections were prepared from four longitudinal points in the depositional lobe. Back-scattered electron images of the sections obtained by scanning electron microscopy were processed and analyzed by mapping of grain fabric using an automated image-analysis procedure. Although the samples appear structureless by macroscopic observation, the grain-fabric map reveals a range of sedimentary features, including distinctive lineations from lower-upcurrent to upper-downcurrent in the most proximal section representing synsedimentary thrusts, a steepening-upward trend of grain imbrication angle in intermediate samples with very low-angle imbrication in the basal horizon, indicative of high-shear-rate flow, and complex imbrication features in the most distal samples. This analysis reveals that massive debris-flow deposits actually contain a range of distinctive structures which are characteristic of the mode of deposition and which are not identifiable by visible inspection or analysis of grain size or color. The proposed method is therefore of great utility for the investigation and characterization of massive deposits

Tidal growth patterns and growth curves of the Miocene potamidid gastropod Vicarya yokoyamai

Volume: 3Start Page: 193End Page: 20

A Holocene sea-level curve constructed from a single core at Osaka, Japan (A preliminary note)

A relative sea-level curve has been drawn based on 25 AMS 14C ages and paleodepths inferred from ostracodes in a Holocene core from Kitatsumori, Osaka, Japan. This is the first relative sea-level curve constructed from a single continuous core in siliciclastic sediments. The new curve indicates that the first flooding at this site was -21.5 m in depth below present mean sea-level at about 9200 calendar years B.P., that the maximum sea-level highstand of about +1.5 m was at 5500 to 5000 calendar years B.P. (about 800 years younger than previously thought), and that a relative sea-level decrease of about -1.2 m took place at about 2200 calendar years B.P. and that a relative sea-level increase of about +0.7 m occurred about 1700 calendar years B.P