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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 904

Last Page: 904

Title: Shelf Break on Modern Passive Margins: Structure, Sedimentation, and Progradation: ABSTRACT

Author(s): Gilbert Boillot, Denis Mougenot, Jeanpierre Rehault

Article Type: Meeting abstract


The time-integrated structural-stratigraphic configuration of the shelf-to-slope break of many modern margins records the interplay of tectonics, submarine erosion and/or depositional processes. A simple process-response model may be used to help interpret the variations of shelf-break configuration and progradational patterns of passive continental shelves. The key factors are (a) the amount and nature of the sedimentary flux (F) provided to and across the shelf, and (b) the depth at which particles come to rest (H), which is largely a function of the local hydrodynamic and boundary layer conditions and of the grain size and density of the particles being transported. By maintaining factors F and H as constants, we can evaluate the role of structural displacement and imp rtance of the relative position of the shelf surface to sea level in the development of the shelf-to-slope configuration.

In places where a shelf subsides, or when there is a demonstrable eustatic rise while an ample sediment supply is provided, a sediment layer may accumulate over much of the shelf; excess seaward-transported sediment will accumulate at and beyond the shelf break. If a shelf remains relatively stable or if there is an appreciable eustatic drop in sea level, much of the sediment can bypass the shelf and will accumulate beyond the shelf break, on the slope, rise, and abyssal plain. As equilibrium is attained, we can expect that D (shelf depth) <= H on a continental shelf, and D > H on a continental slope. Thus, in this example, H becomes coincident with the depth at the shelf break.

The model is tested at shelf-slope interfaces on the Tuscany and Ligurian margins in the western Mediterranean, and on the Iberian margin in the eastern Atlantic. Seismic profiles indicate that the structural-stratigraphic configuration and progradational patterns at shelf breaks observed on subbottom profiles are variable. We correlate this variability with age and tectonic development of a margin, and thus with the successive structural stages through which a passive margin evolves.

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Copyright 1997 American Association of Petroleum Geologists