STRUCTURAL AND STRATIGRAPHIC FRAMEWORK OF LAKE TURKANA, KENYA: AN INTEGRATION OF BASIN-SCALE MULTICHANNEL AND HIGH-RESOLUTION SEISMIC REFLECTION DATA

The Lake Turkana Rift occupies the northern part of the Kenya rift system, and sits in the topographically low depression between the Kenya and Ethiopian domes. A structural and stratigraphic analysis of the offshore part of the basin has been conducted using four different vintages of seismic reflection data. A deep-penetrating, low-resolution, multi-channel seismic (MCS) data set collected in 1984 is integrated with three shallow-penetrating, high-resolution data sets: a set of 1 kHz “Boomer” analogue records collected in 1984, modern digital CHIRP data collected in 2009 and 2010, as well as a small-airgun, single channel data set acquired in 2010. From this analysis, it is observed that this lake consists of three main linked, half-graben basins, each structurally controlled by a boundary fault opposed by a flexural margin. All three basins are impacted by magmatic activity, manifested as extensive disturbances in sub-bottom reflections, particularly in the southernmost basin, as well as extrusive volcanic islands in all three structural basins. Acoustic basement in the basin-scale MCS may be volcanic material, rather than Precambrian crystalline bedrock as is observed in other East African lakes. Numerous normal faults are traceable across long distances within the southern basin. All the faults appear to be basement-involved or associated with volcanic activity.

Three main seismic sequences are identified in the MCS data. These indicate multiple changes in sedimentation that can be accounted for by rapid changes in basin subsidence, widespread volcanic activity, or drastic changes in lake level through time. Each is defined by erosional truncation likely associated with subaerial exposure in some cases. Preliminary interpretations of the high-resolution data reveal several prominent reflections that are thought to correspond to recent lowstands, and possibly even lake desiccation. On-going study of the high-resolution dataset includes obtaining “ground truth” data through analyses of newly acquired piston cores and vibrocores.