Question #086c8
1 Answer
no one really knows.
Explanation:
The theories of Epeirogenic movements are designed to explain the how ocean, and deep ocean sediments in thick layers came to be part of the continental crust.
According the classic plate tectonic, it seems impossible for ocean and deep ocean sedimentary layers to found in thick undisturbed layers on the continents. When the Ocean plates meet Continental plates, the Ocean plates are pushed underneath the Continental plates. and melted. These subduction zones are well known and documented.
Some ocean sediments are found on top of mountains. these can be explained as locations where convergent boundaries cause the deformation of the crust. The pressure of the convergent boundaries causes the crust to buckle pushing the ocean layer up.
The presence of the thick sedimentary layers laying flat and undisturbed on the continents is difficult to explain.
The interior of continents are thought to have subsided allowing marine incursions. These marine incursions would be the source of the ocean sediments on the continents. The question is how the layers were later uplifted.
One answer is that the magma from the mantle is pushed into the crust under the continents causing a slow uniform uplift over a broad area of the continents. While there is no empirical evidence of this theory it is used to explain how the marine sediments could have been formed and lifted to there present locations on the continents.
