--> ABSTRACT: Structural Segmentation and Seismic Stratigraphy of the Kavala Island Ridge Accommodation Zone and Its Adjacent Half-Grabens, Lake Tanganyika, East African Rift System, by Kiram E. Lezzar and Christopher A. Scholz; #90906(2001)

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Kiram E. Lezzar1, Christopher A. Scholz1

(1) Syracuse University, Syracuse, NY

ABSTRACT: Structural Segmentation and Seismic Stratigraphy of the Kavala Island Ridge Accommodation Zone and Its Adjacent Half-Grabens, Lake Tanganyika, East African Rift System

The Kavala Island Ridge (KIR) is a subaqueous horst that separates deeply-subsided half-graben basins in Lake Tanganyika. Each half-graben is filled with up to 5 km of syn-rift lacustrine sediment. The ridge strikes obliquely to the rift axis, is about 12 km-wide and extends for ~65 km across the rift. About 1100 km of basin-scale and 2650 km of intermediate-resolution (50-500Hz) seismic reflection data are used to constrain the structural segmentation and sequence stratigraphy of this accommodation zone.

The ridge shows marked cross-sectional and along-strike asymmetry. Its western border fault is composed of discontinuous fault segments (each ~15 km long), whereas the eastern border fault is bounded by a single continuous fault. Fan-shaped sedimentary sequences suggest that subsidence of the adjacent half-graben basins was syn-depositional. We observe limited subsidence adjacent to the single-segment eastern border fault, compared to more than 800 m of basement subsidence adjacent to the western margin of the KIR.

The offset on the border fault changes along strike, which leads to marked variations in depositional processes on either side of the ridge. Where there is limited subsidence, we observe chaotic to sub-transparent units which are interpreted as platform/slope deposits (deltas, channels and debris flows). Along deeply subsided margins, extensive, fan-shaped, stratified units develop.

Sediment thickness varies markedly atop the ridge (0-630 m), with linked faults located near the western side of the ridge controlling the development of perched sub-basins. Chaotic to sub-transparent units (5 km-length, 1.5 km-wide and 50-300ms-thick), interpreted to be coarse-grained sediments, are observed adjacent to perched fault segments. These are interpreted as proximal detrital talus deposits, that alternate with stratified, organic-rich, fine-grained sediments.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado