Sequence Stratigraphy and Eustatic Sea Level

Michelle A, Kominz: Department of Geosciences, Western Michigan University, Kalamazoo, MI; and Stephen F. Pekar: Lamont-Doherty Earth Observatory, Palisades, N.Y.

Abstract

A number of the basic tenets of sequence stratigraphy tie to the relationship between sequence architecture, water depth, and sea-level change. Testing of these tenets is made particularly problematic as a result of the recent and prevalent assertion that it is impossible to obtain eustatic magnitudes from sequence stratigraphic data. Although much qualitative data has been amassed to define and corroborate the sequence model, we present the first quantitative tests of the model.

Two-dimensional backstripping of strata in a sequence stratigraphic framework coupled with quantitative benthic biofacies analyses has yielded the first quantitative estimates of the geometry and water depths of ancient, prograding sequences. The data set is from Oligocene strata beneath the New Jersey Coastal Plain. Borehole data, largely from Ocean Drilling Project Sites 150X and 174AX, provided excellent recovery for quantitative estimates of age, lithology, compaction, and benthic biofacies.

Results indicate that in most cases, sequence boundaries are associated with local downward shift in base level (sea-level fall) as predicted by most sequence models. However, maximum flooding surfaces generally occur at or near the maximum value of sea-level rise, rather than at the maximum rate of sea-level rise. Finally, there is not a consistent relationship between clinoform breaks and water depth.