| Abstract: | The boundaries between major world-wide sequences of sediments on continental platforms are due primarily to either eustatic changes or to systematic uplift of the continental interior. If thermal contraction of the lithosphere controls basin subsidence, basins would continue to subside during times of low eustatic sea level. Calculations indicate that significant gaps in the geological record could be produced by modest eustatic sealevel changes even in rapidly subsiding basins. For example, a 95 m withdrawal could have produced the sub-Devonian unconformity in the Michigan Basin. The vertical amplitude of eustatic variations can be determined directly from the depth of paleotopographic valleys (135m for sub-Pennsylvanian of Illinois Basin) and from the present elevation of sediments deposited during highstands (300 m above present sea level). The Illinois Basin aparently continued to subside during the sub-Pennsylvanian regression. |
