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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 30 (1946)

Issue: 2. (February)

First Page: 249

Last Page: 253

Title: Origin of Continental Shelves

Author(s): J. H. F. Umbgrove (2)


In order to explain the common occurrence of a shelf edge at the isobath of 200 meters, a widespread subsidence of the shelf area in the order of 100 meters has to be assumed, apart from the influence of eustatic changes of sea-level. Spasmodically a warping or tilting movement has taken place along the continental border, causing a submergence of what formerly was the margin of the continent and a simultaneous bowing-up of a marginal tract parallel with the newly formed coast line. The most recent movements are revealed by the attitude of the marine terraces occurring along oceanic coasts in far distant regions. It is argued that the periodical action of convection currents, displaying themselves below the continental margin as a result of the existing distribution of si lic and simatic rocks in the border zone of continental and oceanic areas, accounts for the periodical movements along the marginal flexure of the continents. So, the phenomena of the continental margin are correlated with other periodic events occurring in the earth's crust and its substratum. Finally a section is devoted to the submarine canyon-like trenches which are incised in the shelf body. These features are classified in three groups. Theories involving a subaerial origin of the notched shelf edge are incompatible with data presently known about the geological history of the continental margin.

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