QUANTIFICATION OF THE EFFECTS OF EUSTASY, SUBSIDENCE, AND SEDIMENT SUPPLY ON MIOCENE SEQUENCES, U.S. MID-ATLANTIC MARGIN

Stratigraphers have long sought to quantify the effects of eustasy, subsidence, and sediment supply on the development of the stratigraphic record, but the relative controls of these processes even on passive continental margins remains controversial. Previous sequence stratigraphic studies of the New Jersey margin have established that the primary control on Miocene sedimentation is eustasy, determining the global template of available sequences. Comparison of Miocene sequences in New Jersey, Delaware, Maryland and backstripping of Delaware and New Jersey sections demonstrates that sediment supply also controls the preservation and thickness of sequences through its influence on loading subsidence. Miocene facies are wave-dominated in Delaware and deltaic in New Jersey, though both regions share a similar sequence stratigraphic framework for the Miocene. Sequences can be correlated throughout this region with a Sr-isotopic chronology (±0.6 to ±1.2 m.y.); eight Miocene sequences correlate regionally and can be tied to global oxygen isotopic increases, indicating a glacioeustatic control. Backstripping quantifies eustatic and subsidence effects; it documents that a period of excess subsidence began at Bethany Beach at ca. 21 Ma and continued until 12 Ma, with maximum rates from ~21-16 Ma. We attribute this enhanced subsidence to local flexural effects responding to the progradation of thick sequences through this area. Subtracting excess subsidence from the Bethany Beach backstripped R2 curve yields a record that is remarkably similar to New Jersey eustatic estimates. We conclude: 1) Miocene subsidence differences on this passive continental margin are caused by accommodation changes associated with flexural loading; and 2) although overprinted by sediment supply and flexural loading effects, it is clear that the eustatic signal is still well-expressed in continental margin stratigraphic records.