Angola Basin

Typically divergent boundaries are described as having landward extension, seaward contraction, and translation, however the order of events in this area are difficult to distinguish in such a clear-cut manner. This spreading mechanism requires at least some deformation as opposed to the breakup of rigid blocks. The driving force behind salt tectonics is thought to be extension governed by gravity. Seismic profiles taken from offshore Angola show many different salt structures such as diapirs, clines, turtle features, and salt walls that show several deformation phases as the salt squeezes upwards when it is deposited upon. Many of the salt forms are associated with early Cretaceous folding and uplift as well as lateral shortening. In the basin this tectonic mechanism is attributed to three periods of high strain that occurred at approximately 96, 28, and 10 million years ago, and the most recent high strain activity is still ongoing. These high strain rates lasted anywhere from 15 to 36 million years while rafting itself lasted from 7-10 million years. ==Geologic history==

Mesozoic The formation of the Angola Basin can be divided into three phases of rifting which took place from approximately 145-113 million years ago from the Jurassic to the Cretaceous. After the rifting, salt deposited upon the preexisting bedrock. The sedimentary fill from the Congo River created a large deep-sea fan where the river enters the ocean, and this fan is still one of the basin's most predominant features. From the beginning of the Quaternary to present day much of the sediment is influenced by the Walvis Ridge, a hotspot trail that extends several hundred kilometers off the coast of Africa into the Atlantic Ocean, in addition to the Congo River. During this time the carbonate compensation depth, the depth at which carbonates dissolve, is at a minimum depth of 5400 m, over 1000 meters more than the average depth. ==Subbasins==

Lower Congo Basin The Lower Congo Basin lies in the northern region of the Angola Basin and is largely identified by a sedimentary fan that is fueled by the Congo River and is part of the Ogooue Delta. Since the fan is mainly composed of turbidite deposits composed for large amounts of sandstone and fine grained muds, it is likely an area that is currently generating hydrocarbons and probably has been for the past 30 million years. Kwanza Basin The Kwanza Basin lies in the lower region of the Angola Basin and can be divided into the inner and outer Kwanza Basins, with the inner basin lying closer to the continent of Africa and the outer basin surrounding the inner basin. These are areas where the signature salt layer is very thin or absent from the stratigraphic record. The basin's topographic features are mainly affected by salt tectonics, since the salt in most areas was originally over one kilometer thick. There are two main types of salt structures found in the inner Kwanza Basin: narrow salt walls which developed from salt-cored folds, and broad salt walls that formed likely due to major uplift in the area. Many of the salt features dissolved over time which led to the development of sedimentary troughs in the Cenozoic, although fewer troughs did develop as a result of extension. ==Hydrocarbons==

The basin houses economically important hydrocarbon reservoirs that serve as a source of petroleum. In December 2000 a research expedition collected gas hydrate specimens from one of the world's largest pockmarks located in the Congo-Angola Basin. The depression was 800 meters in diameter and located 3160 meters below sea level and developed as a result of several smaller pockmarks collapsing into each other. The majority of the hydrocarbons found were gas hydrates composed of 100% methane. ==References==