Oligocene to Middle Miocene Sr-Isotopic Stratigraphy of the New Jersey Continental Slope

Abstract

We analyzed specimens of mixed planktonic foraminifer species for Sr isotopes from the Oligocene to middle Miocene sections from boreholes (Ocean Drilling Program Sites 902, 903, 904, and 906; and outcrops on the New Jersey continental slope. We concentrated on the upper Oligocene-middle Miocene at Sites 903 and 904 (444 and 1129 m present water depth, respectively), the upper Oligocene-lowermost Miocene at Site 902 (811m water depth), and slope outcrops in Carteret and Lindenkohl canyons. Sr-isotopic age estimates of the Ocean Drilling Program boreholes provide a good stratigraphic framework for upper Oligocene to middle Miocene sections, overcoming problems with rare calcareous plankton zonal markers. When integrated with ongoing biostratigraphic and magnetostratigraphic studies, the Leg 150 sites will provide a precise chronology of slope reflectors that also correlate with sequences boundaries traced under the continental shelf. Preliminary integration is encouraging: (1) nine of the 10 Oligocene to middle Miocene slope reflectors (sequence boundaries) correlate with global δ 18 θ increases and with sequence boundaries in the onshore New Jersey coastal plain, arguing for a causal link between formation of sequence boundaries and glacioeustatic lowerings; and (2) several hiatuses on the slope also correlate with reflectors and the major δ 18 θ increases, although many of the seismic reflectors appear to be conformable at the slope boreholes. Outcrop studies date a major change in depositional regime in the earliest Oligocene; this "siliciclastic switch" from an Eocene carbonate ramp to a starved siliciclastic early Oligocene margin correlates with a global δ 18 θ increase and a regional cooling. Sediment starvation in the early Oligocene resulted in a poorly preserved record on the slope. Sedimentation rates subsequently increased in the middle Oligocene on the entire margin, when prograding clinoforms appeared beneath the modern shelf and rates increased again in the early to middle Miocene. We attribute this progradational change to lower long-term sea level, although hinterland tectonics may have played an important role.

Cenozoic global sea level, sequences, and the New Jersey Transect: Results From coastal plain and continental slope drilling

“…The early to middle Eocene on the New Jersey margin was strongly influenced by pelagic carbonate deposition, minimal siliciclastic input, warm paleoclimates, and a gentle ramp-shaped physiography. A switch from pelagic carbonate to siliciclastic sedimentation occurred in two steps: carbonate production shut down onshore in the late middle Eocene [Browning et al, 1996]; on the slope, carbonate production declined in the earliest Oligocene [Miller et al, 1996b] (Figure 14)]. Additional drilling on the New Jersey margin is needed to provide better estimates of sea level amplitudes, to continue to evaluate the ages and phase relationships of glacioeustatic changes to margin response, to test shelf facies models, and to extend our sequence stratigraphic studies to the supposedly ice-free, "greenhouse" Cretaceous.…”

Effects of relative sea-level changes on the diagenesis of Eocene sediment: New Jersey slope and coastal plain

“…These observations suggest that diagenetic transformations in the slope sediment are to a great extent influenced by large-scale sedimentation changes in the margin such as the switch from Eocene pelagic carbonate to Oligocene hemipelagic siliciclastic sediments. The more accentuated sea-level lowerings that occurred in response to global cooling and possible tectonics (Miller et al, 1996b) from the early Eocene to the Oligocene contributed to the changes in mineral content, fluid character, and diagenetic transformations at the slope sites.…”

“…sponse to the changing character of the fluids and surficial sediment. Sediment progradation, that increased in the middle Oligocene and contributed to the transport of terrigenous sediment further offshore, has been correlated to a global δ 18 O increase and a regional cooling, to a long-term sea level lowering, and to possible tectonics (Miller et al, 1996b). These observations suggest that large-scale, diagenetic changes in deep sea slope sediment occur in response to long-term, margin-wide events such as the Oligocene eustatic lowerings.…”

“…A third major unconformity separating the upper Eocene from the upper Oligocene has been recognized at all slope Sites (Mountain, Miller, Blum, et al, 1994;Aubry et al, 1996). Seismic Reflection o1, that marks the unconformable surface, has been correlated with a global δ 18 O increase in regional cooling (Miller et al, 1996b) and represents a sequence boundary. This unconformity coincides with a significant change in the sediment depositional regime of the margin from carbonate-dominated pelagic during the Eocene to hemipelagic siliciclastic sediment during the Oligocene (Mountain, Miller, Blum, et al, 1994).…”

“…Although the major focus of the New Jersey sea-level transect was on the Oligocene to Holocene depositional sequences, drilling also penetrated Eocene sediment. Unconformities occur on the margin that document relative sea-level lowerings during the Eocene on the coastal plain and slope (Olsson and Wise, 1987;Poag and Low, 1987;Miller et al, 1990;Miller et al, 1996b;Browning et al, Chapters 17 and 18, this volume). An extensive array of seismic lines permitted the correlation of seismic reflections from the slope to the shelf and to sequence boundaries, and document a glacioeustatic lowering at the Eocene/Oligocene boundary.…”