Recent geological fieldwork, radiometric age dating of volcanic rocks, gravity and seismic reflection surveys have considerably refined our understanding of the tectonic evolution of the northern Kenya Rift. These data reveal that deep, half-graben basins up to 7 km thick were initiated west of Lake Turkana probably during Late Oligocene-Early Miocene times. The basins, bounded by easterly dipping faults, trend along the western side of the rift from Lake Turkana to the Elgayo Escarpment-Tugen Hills area. Some rift basins were episodically active from the Oligocene to the Pliocene while others were only active for a few million years. Some sag basins may have developed during periods of rifting quiescence. In the Turkana area the location of faulting gradually shifted eastwards with time. Volcanism both preceded and accompanied rifting. Within the Turkana area, volcanism moved south and east with time, beginning about 33 Ma (probably preceding half graben formation by a few million years) and continued to the present day. Extension along faults is greater in the Turkana area (between 25-40 km) and decreases southwards to probably 5-10 km or less in the southern Kenya rift. This pattern of extension values agrees with deep seismic refraction work (KRISP), which indicates thin crust in the Turkana area (about 20 km) that thickens to about 35 km south of Lake Baringo. The extension values, crustal thinning, age of volcanism and the timing of faulting to the south all point towards a southerly propagation of the rift.

Exploration in the Rukwa rift, using gravity and seismic reflection surveys, fieldwork, and drilling has defined the structure and stratigraphy of the basin in greater detail than any other part of the Western rift. The stratigraphy comprises Precambrian basement, Karroo sandstones, shales and coals, upper Miocene red beds, and Miocene‐Recent lacustrine and fluvial sediments. During Miocene‐Recent rifting the greatest sediment input apparently came from axial fluvial systems flowing from the northwest and southeast. The southwestern area experienced alternating shallow lacustrine and fluviodeltaic conditions during the Miocene‐Recent. Cenozoic age rift structures have a dominant NW‐SE and a subordinate N‐S trend. The NW‐SE trend tends to follow a Precambrian basement and later Karroo structural trend. NE‐SW seismic lines indicate up to 10 km extension of the Tertiary section in a direction oblique to the probable E‐W regional extension direction. In the southeastern portion of the basin both Karroo and Tertiary‐Quaternary sediments expand into the Lupa fault zone, reaching thicknesses of up to 3 and 7 km, respectively. Tertiary‐Quaternary sediment thicknesses decrease northwestward, accompanied by a decrease in the amount of extension and a broadening of the basin as extension is transferred to the Lake Tanganyika rift.

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The Wagwater Trough is a fault‐bounded basin which cuts across east‐central Jamaica. The basin formed during the late Palaeocene or early Eocene and the earliest sediments deposited in the trough were the Wagwater and Richmond formations of the Wagwater Group. These formations are composed of up to 7000 m of conglomerates, sandstones, and shales. Six facies have been recognized in the Wagwater Group: Facies I‐unfossiliferous massive conglomerates; Facies II—channelized, non‐marine conglomerates, sandstones, and shales; Facies III‐interbedded, fossiliferous conglomerates and sandstones; Facies IV—fossiliferous muddy conglomerates; Facies V—channelized, marine conglomerates, sandstones, and shales; and Facies VI—thin‐bedded sheet sandstones and shales. The Wagwater and Richmond formations are interpreted as fan delta‐submarine fan deposits. Facies associations suggest that humid‐region fan deltas prograded into the basin from the adjacent highlands and discharged very coarse sediments on to a steep submarine slope. At the coast waves reworked the braided‐fluvial deposits of the subaerial fan delta into coarse sand and gravel beaches. Sediments deposited on the delta‐front slope were frequently remobilized and moved downslope as slumps, debris flows, and turbidity currents. At the slope‐basin break submarine fans were deposited. The submarine fans are characterized by coarse inner and mid‐fan deposits which grade laterally into thin bedded turbidites of the outer fan and basin floor.