COMPARISON OF GREENHOUSE VS. ICEHOUSE SEA-LEVEL AMPLITUDES AND SEQUENCE ARCHITECTURE: THE ENIGMA CONTINUES

First-order correlations between oxygen isotopic increases and unconformities have established a close link between sequence boundaries and glacioeustatic lowerings for the past 42 Ma (the "Icehouse" Earth"). The challenge has been to convert this knowledge to a eustatic estimate. Passive margin records provide a direct, but discontinuous record of eustasy that can be derived from backstripping, removing the effects of loading, compaction, and thermal subsidence. Though oxygen isotopes provide a continuous record, the eustatic signal is convolved with temperature changes. The backstripped results among several onshore boreholes yield similar eustatic estimates (R2) for the past 94 m.y., indicating that we have successfully removed the effects of thermal subsidence, loading, and water-depth variations. Though our oxygen isotopic-based glacioeustatic estimates make assumptions about thermal history, they are remarkably similar to the R2 estimates for the past 42 m.y. During the Miocene,10-35 m 3rd order eustatic lowerings are markedly lower than the ~100 m changes purported by Exxon Production Research. Convergence of results from backstripped and isotopic estimates indicates that we have isolated the eustatic component. The Cretaceous to Eocene World has been assumed to be an ice-free "Greenhouse." Backstripping of Late Cretaceous to Paleogene onshore NJ sequence yields amplitudes of 50+ m in <1 m.y., yet only one sequence boundary at the Campanian/Maastrichtian boundary can be tied to global oxygen isotopic increase and inferred glacioeustatic lowering. This is partly due to sparse isotopic records for the Late Cretaceous, but may also reflect the absence of geological evidence for ice sheets. This poses an enigma to sequence stratigraphy because the large, rapid changes in sea-level during this interval can only be explained by glacioeustasy. Onshore NJ Cretaceous to Eocene sequences differ in cyclicity from "Icehouse" sequences, with generally shorter hiatuses and wider facies variations for a narrower water depth variations. Though this may reflect different mechanisms, it still fails to explain the abrupt nature of Cretaceous sequence boundaries.