ESTIMATING SHORT-TERM CHANGES IN EUSTATIC SEA LEVEL

The history of short-term eustatic sea level change proposed by P. R. Vail and his coworkers was originally based on shifts through time in the landward pinchout of seismic sequences. In order to quantify the magnitude of these proposed sea level changes, histories of subsidence, sediment loading, sediment compaction and paleowater depth are required. Of these, accurate estimates of paleowater depth and subsidence are the most difficult to derive. This approach is applied to two example data sets. For one study, the Midway Atoll, we use the theoretical subsidence model of Detrick et al. (1981). The possible error in this model is approximately the same as the extreme differences in sea level highstands (50-100 m) proposed by previous investigators. The second example is from the Baltimore Canyon area. Here we estimate subsidence by an average angular tilt rate. Resulting estimates of sea level highstands for the past 30 Ma are similar to the long-term sea level estimates of Kominz (1984); however, the overall variation in the highstands parallels that of Haq et al. (1987). Short-term sea level falls are estimated to be similar in magnitude to those of Haq et al. (1987). Most of these short-term fluctuations are within the range of reasonable glacioeustatic fluctuations (30-100 m). A correlation is found between the estimated short-term changes in sea level and the Miocene oxygen isotope record. This correlation exists both prior to and after 14 Ma; however, there is a 1.08 parts per thousand isotopic shift in the data in the Middle Miocene. Because estimated highstands are within 10-15 m of being the same magnitude before and after this shift, we suggest that this shift is caused mainly by a cooling of deep waters.