Abstract
Dent numerous Holocene sea-level curves have hitherto been published for various parts of the world. In this paper, about twenty such curves were selected and discussed. It is considered that the following two opinions discussed by Shepard (1964), Guilcher (1969), Fairbridge (1971) and others are the subject of the greatest controversy, although there are several clear disagreements among these curves as shown in Figs. 1_??_4. 1. When had the eustatic sea-level reached at the highest level? 2. Has the sea-level risen with minor fluctuations or without? Based on these two different standpoints, the curves can be classified into the following three types: (a) that in which the eustatic sea-level had risen above the present level with fluctuation (provisional name: high sea-level with fluctuation gro up, e.g. Fairbridge, 1961; Mörner, 1969; etc.); (b) that in which the present is the highest level and the sea-level has fluctuated (low sea-level with fluctuation group, e.g. Ters, 1973; Greensmith & Tucker, 1973; etc.); and (c) that which recognizes neither a high sea-level nor fluctuations (smooth group, e.g. Shepard, 1964; Scholl et al., 1969; etc.) (a) and (c) correspond to the curves known as the “Fairbridge Curve” and “Shepard Curve” respectively.
Concerning about the standpoint 1, since Daly (1920) recognized previous shorelines a few feet above the present sea-level for various parts of the world and claimed that such shorelines were the result of ecstasy, many scientists have recognized this so-called “Daly's level”. However, various scientists, mainly those in the United States and Europe, have opposed this idea using the data obtained from North America and Europe, and have claimed that the present sea-level represents the highest level in the Holocene. The controversy on high sea-level during the Holocene period thus constitutes the most interesting problem.
Compiling the data on Holocene sea-level changes from areas which were considered locally stable, the author mapped areas where the present sea-level was reported as the highest level and those where the sea level was considered to have risen above its present level in the Holocene respectively (Fig. 5). As a result, regionality with continental scale were recognized: in North America and part of Europe, the present sea-level is the highest in the Holocene, whereas in South America, Africa, Asia, and Australia, a high sea-level is generally recognized. Such differences have been also recognized by Gill (1971), etc., who claimed that this problem should be discussed on a continental scale. However, no concrete explanation has yet been put forward. It is interesting to note that such differences over wide areas have been well explained on the basis of broad crustal movements effected by glacio- and hydro-isostasy as recently stated by Walcott (1972). As shown in Fig. 5, most part of North America and Europe, where the present sea-level is the highest, represents the peripheral zone of the former ice sheets and have submerged by glacio-isostasy, whereas the regions where the sea-level has risen above its present level in the Holocene out have been uplifted by hydro-isostasy. If this explanation of the problem relating to high sea-level by glacio-and hydro-isostasy is justified, it is thus not significant to discuss the problem further from the eustatic point of view.
As for the standpoint 2, judging from the data in Table 1, it appears that the difference between a fluctuating curve and a smooth curve does not result from local conditions in the area (e.g. landform, local crustal movements, tidal range, etc.) or the methods employed for determination of the altitude and age of the past sea-level. It might be resulted from the fact that the indivisual researcher's appraisal of errors contained in the altitude and age of past sea-levels has played an important role.
