Figure 2. Example of a buried middle Miocene clinoform (m2c, ~12.5 Ma) mapped using a commercial seismic grid available from the New Jersey margin (see Fig. 1). Lower panel: structure map showing a seismic grid, indicating existing drill Sites 902-904, 906 (Leg 150) and 612 (Leg 95), and Mid-Atlantic Transect (MAT) drill sites 8B, 9B, and 13A (Leg 174A). Site MAT-7B was proposed, but was not approved for Leg 174A drilling. Contour interval units are milliseconds two-way traveltime below present sea level. Upper panel: 3-D perspective shaded image with traveltime contours (azimuth of artificial illumination = 220°). Both panels are viewed from an azimuth of 180° and an elevation of 30°. The clinoform slope canyon is V-shaped; the mapping reveals an apparent downslope continuation of this drainage feature (from Fulthorpe and Austin, in press).
Figure 3. Ewing 9009 MCS profile 1002; Leg 174A shelf Sites MAT-8B and MAT-9B are located approximately along this line, as shown, as is secondary upper slope Site MAT-13A (see also Fig. 1). Note the pronounced progradation of late Paleogene-Neogene clinoforms. These clinoforms, and the sea-level signal they hold are the scientific focus of MAT drilling on the shelf. Selected sequence boundaries are labeled, for comparison with interpreted site-specific Oceanus 270 profiles. Upper slope drilling, if it takes place, will augment the results from Leg 150 by adding to existing chronostratigraphic control.
Figure 4. "Hazards-type" MCS surveys completed in 1995 at locations proposed and approved for Leg 174A drilling on the New Jersey shelf: MAT-8B and MAT-9B (see also Fig. 1). Individual profiles are spaced at 150/300 m; the total area of each grid is ~2 km x 2 km. Also included are connecting regional profiles 145, 149, and 247, and the hazards grid for MAT-7B, which was proposed but not approved for Leg 174A drilling.
Figure 5. Comparison of the timing of Oligocene to middle Miocene reflectors on the New Jersey slope with a benthic foraminiferal 18O record, a summary of onshore sequences, and the inferred eustatic record of Haq et al. (1987, after Miller, Mountain et al., 1996a). The 18O record is a stacked composite of Cibicidoides spp. from several sites that has been smoothed to remove all periods >1 m.y.; Oi1 to Mi6 are 18O maxima; dashed lines indicate inflections in the d18O records immediately pre-dating the maxima. Shelf-slope reflectors o1 to m1 are dated on the New Jersey slope (Leg 150) and are shown with best age estimates (indicated with thin lines) and error bars (indicated with boxes). Further calibration of these horizons beneath the shelf is the primary objective of Leg 174A. Onshore sequences are indicated by dark boxes; the white areas in between are hiatuses. Drilling on the New Jersey coastal plain is continuing and will be incorporated as Leg 174AX (see Fig. 1). New Jersey onshore sequences O1 to O6 are Oligocene, and Kw0 to Kw-Cohansey (Coh) are Miocene; cross-hatched areas indicate uncertain ages. Sequences TA4.4 to TB3.1 are from Haq et al. (1987).
Figure 6. Diagrams of depth and time vs. distance for idealized clinoform sequences and the optimal strategy for drilling them. The most seaward drill location is most likely to recover a complete record across sequence boundary 2 (SB2), containing biostratigraphic markers known from the deep-sea record; this was the strategy used during Leg 150 and will be continued on Leg 174A at (back-up) upper slope Sites MAT-13A to D (see Fig. 1). The other two locations shown will recover critical shallow-water facies across SB2. The most landward location will recover latest highstand deposits below SB2 (Site MAT-8B); the center location will recover early lowstand deposits above SB2 (Site MAT-9B). Such site pairing is crucial to understanding both the amplitude of sea level changes and the facies associated with clinoform geometries.
Figure 7. Graphical representation of anticipated Leg 174A operations at primary shelf Sites MAT-8B-3 and MAT-9B-1.
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To 174A Primary Site Summaries
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