UTIG Research Projects Archive

Principal Investigators: Craig S. Fulthorpe and James A. Austin, Jr.

Funded by: Office of Naval Research

Documentation of along-strike variations in the morphologies of continental-margin clinoforms is essential for understanding mechanisms of progradation, one of the fundamental relationships between depositional processes and preserved stratigraphy. Maps based on a grid of commercial multichannel seismic (MCS) data offshore New Jersey, extending >70 km along strike and ~50 km down dip, reveal the 3-D morphology and evolution of four buried surfaces correlated with middle-upper Miocene sequence boundaries calibrated by drilling on the adjacent continental slope (Fulthorpe and Austin, 1998). The maps encompass Ocean Drilling Program Leg 174A drill sites on the outer shelf. This work is related to ONR's long-term plan under its STRATAFORM initiative to develop a natural laboratory on this part of the middle Atlantic continental shelf.

Miocene clinoform breakpoints are not depositional analogs of the modern shelf edge. They are linear to gently arcuate; breakpoint and slope trends indicate a systematic southward displacement of depocenters over about 5.6 m.y. Progradation responded to point (fluvial) sediment sources, but efficient along-strike sediment dispersal muted their influence. Canyons are absent on three of four clinoform slopes; the fourth has one V-shaped canyon and a broad erosional area (possible slope failure?). Planar-floored canyons also occur, albeit rarely, seaward of clinoform toes. Apparently, V-shaped and planar-floored canyons, previously ascribed to downslope erosion vs. slope failure/headward erosion, respectively, can coexist. The accretionary northern slope of Little Bahama Bank is a possible morphologic analogy. By analogy with Pleistocene shelf/slope geometries, an absence of canyons breaching clinoform breakpoints suggests that rivers did not discharge at paleo-shelf edges, indicating that sea-level lowstands postulated for the middle-upper Miocene did not expose breakpoints. Reconstruction of breakpoint paleo-elevations supports this conclusion for three of the four mapped horizons, suggesting that elevations of some Miocene lowstands on the global sea-level curve are too high by up to 60 m.

Interpretation of profile A157 which passes through the ODP Leg 150 drilling area.
Sequence boundaries o1*, m3*, m2*, m1* and m0.5* are approximately correlative
with sequence boundaries o1, m3, m2, m1 and m0.5 of Mountain, Miller, Blum, et al. (1994).