Gravitational collapse at continental margins: products and processes; an introduction

Abstract

Gravitational collapse can occur on many scales on submarine slopes. As hydrocarbon exploration has stepped into increasingly deeper water geologists have realized that entire sedimentary prisms on continental margins are deformed by structures that do not penetrate into the underlying crust. In this respect, large-scale gravitational deformation systems at continental margins bear many similarities to deformation in orogenic thrust belts. Also like thrust belts, they exhibit an overall wedge-shaped geometry, suggesting that critical taper theory exerts a first-order control over their formation, and their development is controlled partly by complex feedbacks between the evolving deformation system and the synkinematic (‘syntectonic') stratigraphy. However, unlike orogenic thrust belts, deformation at continental margins is not directly linked to stresses generated at plate margins but rather reflects gravitational instability of the sedimentary pile itself. In effect, submarine slopes are in a state of landslip or flow with generally extensional faulting on the upper slope and continental shelf coupling with contractional structures at the slope toes. These systems can be hundreds of kilometres wide, the scale of many tectonically driven mountain belts (see review by Rowan et al . 2004). As the exploration for oil is revealing thin-skinned gravitational deformation from many sites around the world, it is increasingly seen as a key structural–stratigraphic component of continental margins. Linked extension–contraction deformation systems potentially offer ideal natural laboratories for understanding the accommodation of lateral contraction in poorly lithified sediments (e.g. Butler & Paton 2010). Consequently, there is now substantial interest in the structural evolution of these large-scale systems. Although the products of large-scale gravitational failure, especially deep-water thrust belts, are the focus of extensive exploration efforts by oil and gas companies, there are few descriptions beyond the classic examples of the US Gulf of Mexico …