Cenozoic global sea level, sequences, and the New Jersey transect: Resultsfrom coastal plain and continental slope drilling

The New Jersey Sea Level Transect was designed to evaluate the relationship s among global sea level (eustatic) change, unconformity-bounded sequences, and variations in subsidence, sediment supply, and climate on a passive co ntinental margin. By sampling and dating Cenozoic strata from coastal plain and continental slope locations, we show that sequence boundaries correlat e (within +/-0.5 myr) regionally (onshore-offshore) and interregionally (Ne w Jersey-Alabama-Bahamas), implicating a global cause. Sequence boundaries correlate with delta(18)O increases for at least the past 42 myr, consisten t with an ice volume (glacioeustatic) control, although a causal relationsh ip is not required because of uncertainties in ages and correlations. Evide nce for a causal connection is provided by preliminary Miocene data from sl ope Site 904 that directly link delta(18)O increases with sequence boundari es. We conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since similar to 42 Ma. We speculate that prior to this, the growth and decay of small ice sheets cau sed small-amplitude sea level changes (<20 m) in this supposedly ice-free w orld because Eocene sequence boundaries also appear to correlate with minor delta(18)O increases. Subsidence estimates (backstripping) indicate amplit udes of short-term (million-year scale) lowerings that are consistent with estimates derived from delta(18)O studies (25-50 m in the Oligocene-middle Miocene and 10-20 m in the Eocene) and a long-term lowering of 150-200 m ov er the past 65 myr, consistent with estimates derived from volume changes o n mid-ocean ridges. Although our results are consistent with the general nu mber and timing of Paleocene to middle Miocene sequences published by worke rs at Exxon Production Research Company, our estimates of sea level amplitu des are substantially lower than theirs, Lithofacies patterns within sequen ces follow repetitive, predictable patterns: (1) coastal plain sequences co nsist of basal transgressive sands overlain by regressive highstand silts a nd quartz sands; and (2) although slope lithofacies variations are subdued, reworked sediments constitute lowstand deposits, causing the strongest, mo st extensive seismic reflections. Despite a primary eustatic control on seq uence boundaries, New Jersey sequences were also influenced by changes in t ectonics, sediment supply, and climate. During the early to middle Eocene, low siliciclastic and high pelagic input associated with Warm climates resu lted in widespread carbonate deposition and thin sequences. Late middle Eoc ene and earliest Oligocene cooling events curtailed carbonate deposition in the coastal plain and slope, respectively, resulting in a switch to silici clastic sedimentation. In onshore areas, Oligocene sequences are thin owing to low siliciclastic and pelagic input, and their distribution is patchy, reflecting migration or progradation of depocenters; in contrast, Miocene o nshore sequences are thicker, reflecting increased sediment supply, and the y are more complete downdip owing to simple tectonics. We conclude that the New Jersey margin provides a natural laboratory for unraveling complex int eractions of eustasy, tectonics, changes in sediment supply, and climate ch ange.