Structure and morphology of the Bosumtwi impact structure from seismic reflection data

Abstract

The Lake Bosumtwi impact structure in West Africa offers unparalleled opportunities for the study of cratering processes, as the structure is young (1.1 Myr) and minimally eroded. Because the center part of the structure is covered by Lake Bosumtwi, which is 8 km in diameter and ~70 m deep, it is possible to use marine-type seismic reflection techniques to obtain high-fidelity images of the lake subsurface, including key elements of the impact structure. Eight profiles of multichannel seismic reflection (MCS) data were acquired in a radial pattern across the basin, as well as two other high-resolution seismic reflection surveys. The MCS data show a well-defined central uplift near the north-central part of the lake. Observed within the annular moat surrounding the buried central uplift is a section of post-impact lacustrine sediments more than 300 m thick. The central uplift structure has a diameter of 1.9 km and a maximum height of 130 m above the annular moat. The central uplift has an overall irregular upper surface with a small graben structure. We observe a series of normal faults that extend as much as 120 m into the sedimentary section above the central uplift. We interpret the normal faults to be a consequence of ongoing compaction of the high-porosity materials that comprise the central uplift. The interpreted impact structure surface, defined using seismic reflection data, was combined with regional topographic data from outside the lake in the form of a digital elevation model, which provides a useful perspective of overall impact structure morphology.