Reading of the trigger records of sedimentary events - A problem for future studies

Sedimentary records of various three- to four-dimensional patterns of nature have recently attracted the special attention of many geologists. The dramatic development of rhythmic sequence stratigraphy is a conspicuous recent instance. The significance of event sedimentation in geohistory, however, has not been examined sufficiently. The problem of how to read the records of triggers or thresholds of sedimentary events has been ignored. The difficulty of solving this problem concerns the difference in patterns between natural sedimentary processes and their resulting sediments. Terminological confusion of event deposits is another cause which hinders our taking note of this problem. A few examples of endeavours to discriminate the threshold of sedimentary events are shown by the analysis of two kinds of turbidites of the Mid-Guatemala Trench, the investigation of slump-derived turbidites of the Suruga Trough, and the study of the seismoturbidites in Lake Biwa. Well-focused investigations of features of trigger-known sediments is the best strategy to find the criteria for discriminating the triggers or thresholds based on sedimentary records of various sedimentary events. From this point of view, more detailed studies of the Santorini Eruption-induced homogenites, the K-T boundary impact-induced tsunamiites, together with the Lake Biwa seismic turbidites, are very important. Further efforts should be made to find and investigate as many trigger-identifiable sediments as possible.