I sailed as shipboard paleontologist (dinoflagellate) on ODP Leg 174A (June-July, 1997). The principal aim of our leg was to investigate the link between glacioeustatic sea level fluctuations and the architecture of continental margins, i.e., to test the concepts of sequence stratigraphy on the New Jersey margin.^1,2 Two sites on the mid shelf (88-100 m water depth) and one site on the upper slope (639.4 m water depth) were cored and logged as part of a long-term project to core a transect across the New Jersey margin, including onshore drilling (ODP Legs 174X and 150X) as well as previous legs on the lower New Jersey margin (e.g., ODP Leg 150, DSDP Legs 93 and 95).

I worked the infamous midnight to noon shift in the Paleo Lab, where the biostratigraphers looking for nannofossils and planktonic forams were generally frustrated by the (not unexpected!) scarcity of calcareous plankton in shelf sediments, though they were abundant just beyond the shelfbreak at the last site we cored (Site 1073) on the upper slope. Fortunately, palynomorphs were almost always abundant in shelf sediments, and I was usually able to assign an age to my samples. Laurent de Verteuil's dinocyst zones, which he erected for the U.S. Atlantic Coastal Plain³ and also identified on the New Jersey slope and rise during ODP Leg 150,⁴ were a tremendous help to me in assigning ages to the thick Miocene sequences on the New Jersey margin, and my PhD work⁵ on the New Jersey slope and rise helped me assign ages to the younger units. The downside, which only palynologists can really appreciate, was the long (hazardous and tedious!) processing required, which is particularly frustrating in a setting where quick age picks are essential.

In a sense, I was lucky that we encountered so many drilling problems on the shelf, which let me catch up on my processing and analysis! Our leg really tested the limits of the JOIDES Resolution for several reasons. Shallow water conditions made it more difficult to keep the ship dynamically positioned on the shelf (where the maximum allowable 4% excursion from vertical was only 4 m in 100 m water!), but we were fortunate in having a month of unbroken excellent weather (also great for daily sunbathing and our weekly BBQ's on deck - including the big Fourth of July bash). Because this margin has actually been explored for its hydrocarbon potential, there were real concerns about possible gas traps, so cores (when we recovered them) were immediately tested for hydrocarbons by our shipboard organic geochemists. The thick sequences of relatively clean unconsolidated quartz sand were our biggest problem however, both in maintaining hole stability and in recovering core samples. Core recovery was only 32.2% for the two shelf sites (1071 and 1072), but was (predictably) excellent on the upper slope site (1073), ~99.9%.

We were nevertheless able to identify a number of unconformities which were prominent surfaces on seismic reflection profiles. The best estimates of ages for these surfaces from our shipboard work were 80-250 ka, ~400 ka, 1.7-4.5 Ma, 7.4-11.3 Ma, and >11.3 Ma. Paleoenvironmental interpretations based primarily on benthic foraminifera as well as pollen, dinocyst, and sedimentological data also allowed us to estimate amplitudes of sea level fluctuations. One of the most exciting shipboard discoveries was the recovery of sediments interpreted as estuarine just above the oldest unconformity (m1, >11.3 Ma, late middle Miocene) at Site 1071. These sediments contained very few dinocysts, but abundant pollen and plant detritus as well as some fungal spores and hyphae. The implication is that the top of the sequence developed very close to sea level, suggesting more large-scale sea level fluctuations during the Miocene than many people previously thought.

Back on shore, the 29 scientists who participated in Leg 174A will continue to study the hard-won sediments from the shelf as well as the excellent record of the upper slope, which surprisingly appears to be nearly devoid of mass wasting. In addition to trying to better constrain the age of the sediments (and therefore the span of time represented by the unconformities), I look forward to examining fluctuations in the transfer of sediments and nutrients from the continent to the deep sea in response to sea level change, using terrestrial palynomorphs as a proxy of terrigenous flux. We'll be discussing the results of this work at our planned post-cruise meeting in Utah next summer, and it will give us a chance to get together once more with a great bunch of people that we got to know really, really well (warts and all!) during a month of constant, relentless interaction under stressful conditions.

References

1. Christie-Blick, N., J. A. Austin Jr, et al., in press. Proc. ODP Init. Reps. 174A.

2. Miller, K. G., G. S. Mountain, and the Leg 150 Shipboard Party and members of the New Jersey Coastal Plain Project, 1996. Drilling and Dating New Jersey Oligocene-Miocene Sequences: Ice Volume, Global Sea Level and Exxon Records. Science 272:1097-1098.

3. de Verteuil, L., and G. Norris, 1996. Micropaleontology Vol. 42 (supplement), 172 pp.

4. de Verteuil, L., 1996. Data Report: Upper Cenozoic Dinoflagellate Cysts from the Continental Slope and Rise Off New Jersey. Proceedings of the Ocean Drilling Program, Scientific Results 150, 439-454.

5. McCarthy, F. M. G., 1992. Quaternary Climate Change and the Evolution of the Mid-Latitude Western North Atlantic Ocean: Palynological, Foraminiferal, Sedimentological and Stable Isotope Evidence from DSDP Sites 604, 607, and 612. Unpublished PhD Thesis, Dalhousie University, Halifax, Nova Scotia. 269 pp.
 

---

This article first appeared in CAP Newsletter 20(2):15-17, 1997.