Fluvial Reservoirs

SEDIMENTARY BASINS - AN INTRODUCTION Definition of a sedimentary basin: A sedimentary basin is an area in which sediments have accumulated during a particular time period at a significantly greater rate and to a significantly greater thickness than surrounding areas. (Compare with physiographic basin - a depression in the surface of the land or sea-floor that may or may not be infilled with sediments). Sedimentary basins of one type or another today cover about 70% of the Earth's surface and contain sediment thicknesses that range from about a kilometer to several 10's km. Some basins are geologically young others have existed for 100's million years. Investigations of sedimentary basins have been the result of collaboration between the different disciplines within the Earth Sciences: where geophysics, geochemistry, structural geology, stratigraphy and sedimentology have all played an important part. A major breakthrough was the plate tectonic paradigm, which allowed basins to be classified according to a unifying geodynamic theory. The driving mechanisms of subsidence are ultimately related to processes within the relatively rigid, cooled thermal boundary layer of the Earth known as the lithosphere. The lithosphere is composed of a number of tectonic plates that are in relative motion with one another. The relative motion produces deformation concentrated along plate boundaries which are of three basic types: • • • Divergent boundaries Convergent boundaries Transform boundaries

Divergent boundaries form where new oceanic lithosphere is formed and plates diverge. These occur at the mid-ocean ridges. Convergent boundaries form where plates converge. One plate is usually subducted beneath the other at a convergent plate boundary. Convergent boundaries may be of different types, depending on the types of lithosphere involved. This results in a wide diversity of basin types formed at convergent boundaries. Transform boundaries form where plates move laterally past