ABSTRACT: Stratigraphy, Deposition History and Environments of Deposition of Cretaceous through Tertiary Strata in the Lamu Basin, South-East Kenya and Implications on Hydrocarbon Exploration

NYAGAH, KIVUTI, National Oil Corporation of Kenya, Nairobi, Kenya

The Lamu basin, which is characterized by an extensional tectonic style, is the failed arm of a tri-radial rift system and possesses tectonic and stratigraphic elements in the postrift series that are analogous to those of the Texas Gulf Coast. Development of the southern part of the basin as a passive margin is closely related to considerations of the predrift position of Madagascar and formation of the Indian Ocean basin during Mesozoic times.

Cretaceous and Tertiary strata in the basin comprises an eastward-thickening succession of sediments on which eustatic sea-level fluctuations and a sequence of unconformities related to pulses of transgressive and regressive depositional trends are superimposed. Recognition of these trends has provided the basis for classification of the strata into megasequences representing distinct provinces with regard to time stratigraphy, sedimentation, tectonics, depositional environments, and hydrocarbon potential. Megasequence II includes strata of the Cretaceous and Paleocene, deposited in tidal-deltaic and estuarine settings. These are in ascending order the upper member of the Mtomkuu Formation, the Freretown Limestone, and the Walu Shale. Megasequence III includes strata of the Eocene thr ugh Oligocene, which were deposited in fluvial, deltaic, and restricted-shelf settings. These are in ascending order the Kipini sandstone, the Pate Limestone, the Linderina Limestone, the Dodori Limestone, and the Barren Beds. Megasequence IV includes strata of the Miocene through Pliocene, which were deposited in restricted-shelf and fluvial settings. These are in ascending order the Baratumu Formation, the Kipevu Beds, the Fundi Isa Limestone, the Marafa Beds, the Midadoni Beds, the North Mombasa Crag, and the Lower member of the Magarini sands.

Understanding the depositional history and environments of deposition of these rocks has been crucial for predicting areas with potential hydrocarbon reservoirs and traps.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)