| Abstract: | Ten data sets have been collected from stratigraphical intervals in the Upper Carboniferous of Central Scotland. They represent six structural units and both distal and proximal deltaic environments, plus a meandering river environment. All show a definite tendency towards a linear relationship between the number of deltaic or fluvial cycles and the total thickness of strata in the interval. This relationship is, however, much stronger in sequences laid down in actively subsiding depositional basins than in areas where subsidence is thought to have been controlled by block faulting in the basement or in areas where there is no clearly defined pattern or subsidence. With respect to facies, the relationship is less close in successions that were frequently affected by widespread marine transgressions. The slopes of linear regression lines fitted to the data sets vary much more than had hitherto been supposed. Thus they are no longer thought to provide possible evidence of some ubiquitous underlying process, such as ductile flow in the upper mantle, which affected all the structural units equally. The line which represents proximal deltaic deposits of Westphalian A age in the Kincardine Basin slopes twice as steeply as any of the eight lines representing other dominantly deltaic successions and considerably more steeply than the line representing a succession of Namurian fluvial cycles. Second- and third-degree polynomial regression lines were also fitted to each data set but these generally satisfy little more of the total variation than do the corresponding linear regression lines, and F-test results indicate that the gains are not statistically significant. Eight of the second-degree lines however share a common shape that suggests a general tendency for both deltaic and fluvial cycles to be somewhat thicker in the areas of greatest net subsidence. |
