A new method for extracting water depth, relative sea-level, and eustatic records from onshore New Jersey Oligocene sequence stratigraphy.

摘要

Ten uppermost Eocene through lowermost Miocene (34.2--23.0 Ma) onshore New Jersey Coastal Plain sequences are recognized and dated by integrating Sr-isotopes, magnetostratigraphy, and biostratigraphy. The distribution of the uppermost Eocene to Oligocene sequences is "patchy", in contrast with Miocene sequences where downdip sections are more complete. Three clinoform rollovers identified from the Oceanus 529 seismic profiles, lie between the o1 (Eocene/Oligocene boundary) and the m1 (Oligocene/Miocene boundary) reflectors. They are dated by extrapolation along strike to onshore wells, correlating to onshore sequences O6 (25.7--24.1 Ma), O4/O5 (27.7--25.9 Ma), and O3 (29.2--28.3 Ma). These seismic data and new data from additional wells indicate that the "patchy" distribution results from the progradation of generally thin and areally limited Oligocene sequences.; Backstripping was used to restore the stratal geometry, including heights of the clinoform rollovers. These rollovers, which began during the latest Eocene, migrated across the old Eocene ramp (1:500 paleoslope), forming shelfal gradients similar to the modern (1:1000 paleoslope gradient). They increased in height from ∼ 20 in at the most updip sites ( ∼ 33 Ma), to ∼ 40 m at the downdip sites (27--24 Ma). Knowing the heights of the clinoform rollovers enabled development of a paleoslope model for a number of time slices for the benthic foraminiferal biofacies and the generation of water depth estimates for the stratal surfaces and the benthic foraminiferal biofacies. From this, sea-level changes were determined from 34.0 to 23.0 Ma for New Jersey. Because local tectonics has been estimated, it was possible to extract an eustatic record. This study represented a first in that: (1) lithofacies and biofacies data sets were combined with two-dimensional flexural backstripping results to reconstruct the stratal geometry and estimate eustasy; (2) spatial uncertainties were determined; and (3) the age resolution for each time surface was estimated.; Nine Oligocene sea-level falls observed in the onshore sites were correlated to major increases in benthic and planktonic foraminiferal d18O records, with eight of the benthic and planktonic foraminiferal d18O increases correlating to these sea-level falls. Water depth (corrected for sediment and tectonic loading) estimates across the unconformities range from 30 to 70 m, yielding eustatic estimates of 20-- ∼ 50 m. Three periods of low sea-level occurred at the beginning of the Oligocene (33.5--32.6 Ma), during the "mid" Oligocene (30--27 Ma) and across the Oligocene/Miocene boundary (24--23 Ma).