High-resolution geophysical survey for the exploration of near surface sand resources at the southern Kenyan coast using a multi source strategy
Ane P. Wiersma, P.J.F. Frantsen, P.N.W. Verhoef
The southern coastal zone of Kenya, is formed by a combination of
isostatic and differential tectonic movements and eustatic sea-level
oscillations. This has resulted in a complex setting with interacting
depositional environments and associated morphology. For a large-scale
construction project, sand of sufficient quality is required. Due to
lack of available resources, the potential for nearby sand occurrences
needed to be explored. Because of the complexity and size of this area
a geophysical survey was especially designed to explore near surface
sand occurrences. The survey consisted of a combination of different
acquisition techniques and included a combined high-resolution swath
bathymetry / side-scan sonar system and a chirp sub-bottom profiler.
Over a total of 780 kilometer track length data was acquired with
these systems across the 25 kilometer long and 4 km wide area of
interest.The bathymetric data provide insight in surface processes and
different types of sedimentary environments, such as fan systems and
incised channels. The side-scan-sonar data give an indication of the
surface sediment types, locations of obstructions and rocky outcrops.
From the chirp sub-bottom profiles the thickness and bedding
structures of the buried sediments could be derived and were used to
plan core locations. 79 vibrocores were executed, the sediment logs
were used during the interpretation of the geophysical data. The
combination of different datasets resulted in a synthesis, describing
the evolution of the southern coastal zone of Kenya, improving our
understanding of the sedimentary dynamics en associated depositional
environments. The results show high-resolution information on the near
surface sand resources of the region and also include additional
features of interest of the sedimentary system, such as outcrops that
should be avoided.