Origin and Morphology of Ocean Margins

Abstract

It is likely that the term was coined before its correctness (in terms of crustal rocks) was realized. The ocean floor, as we have seen, is made of geologically young basalt, unlike the continents. The basaltic rock that forms the ocean floor basement is rather close in composition to the mantle rock it came from (see the section on rocks, in the Appendix). Basalt is somewhat heavier than continental rock largely due to its high iron content. The lesser specific weight of the continental mass makes it protrude above the surrounding seafloor (Fig. 3.1). A thick wedge of sediment forms at the resulting boundary between ocean and continent. (In this view much of the shelf is continent.) The sediments may be well layered or strongly deformed, largely depending on the tectonic forces active at the particular margin considered.