The South Lokichar Basin is a

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsidence ...

in Kenya. It is part of the

East African Rift The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of a ...

system, although it is no longer active. Since 2012 it has been the location of a series of oil discoveries by

Tullow Oil Tullow Oil plc is a multinational oil and gas exploration company founded in Tullow, Ireland, with its headquarters in London, United Kingdom. The company is listed on the London Stock Exchange and is a constituent of the FTSE 250 Index. His ...

and its partners.

Geometry

The South Lokichar Basin is a north-south trending

half-graben A half-graben is a geological structure bounded by a fault along one side of its boundaries, unlike a full graben where a depressed block of land is bordered by parallel faults. Rift and fault structure A rift is a region where the lithosphere ...

with the main bounding fault on its western margin. It is approximately 80 km long, 25 km wide and has a maximum depth of over 7 km. The main fault, known as the Lokichar Fault, is relatively low angle and planar in section, although the dip varies considerably along strike from 12° to 60°.

Fill

The basin is filled by a sequence of

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

(possibly as old as

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

) to

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s. There is one major interval of

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic r ...

s near the top of the sequence called the Auwerwer basalts, dated using

K–Ar dating Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potassium ...

as middle to late Miocene in age (12.5–10.7 Ma).

Hydrocarbon exploration

Exploration in the basin began with the Loperot-1 well drilled by

Royal Dutch Shell Shell plc is a British multinational oil and gas company headquartered in London, England. Shell is a public limited company with a primary listing on the London Stock Exchange (LSE) and secondary listings on Euronext Amsterdam and the New Yo ...

in 1992. This found some oil in thin sands, but proved the presence of a good quality and mature

source rock In petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been depos ...

and good quality

reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...

sands. This phase of exploration ended as the company assessed the results as non-commercial. In 2008 Africa Oil Corp acquired a

PSA PSA, PsA, Psa, or psa may refer to: Biology and medicine * Posterior spinal artery * Primary systemic amyloidosis, a disease caused by the accumulation of abnormal proteins * Prostate-specific antigen, an enzyme used as a blood tracer for pros ...

for license 10BB over the basin. In 2010 they farmed out part of their interest to Tullow, who became the operator. In 2012 drilling began with Ngamia-1, which was a major discovery. Subsequently, another eight discoveries have been made, all, like Ngamia, close to the basin bounding fault. There are now sufficient discovered resources for a commercial development. The proposed export route for the oil is the

Kenya Crude Oil Pipeline Kenya Crude Oil Pipeline, also Lokichar–Lamu Crude Oil Pipeline, is a proposed crude-oil pipeline in Kenya. The pipeline will originate in the oil-rich South Lokichar Basin, near the town of Lokichar, in northwest Kenya to end at Port Lamu, ...

References

{{Reflist Cenozoic rifts and grabens Sedimentary basins of Africa Geology of Kenya