GEOPHYSICAL INVESTIGATIONS IN SALDANHA BAY

Summary

Detailed continuous seismic reflection profiling and side-scan sonar surveys were made of the part of Saldanha Bay that lies to the landward of a line connecting Hoedjiespunt and Salamanderpunt (the ‘inner’ bay). Six distinctive subsurface units (Q-units) were recognized in the seismic records. They were correlated with a sequence of lithologically distinctive units encountered in boreholes drilled in the bay. At any instant in time the sea abrades the sea floor above a certain limiting depth and deposits materials below that depth. The incursion of the sea into an area therefore leads both to the removal and deposition of materials. The borehole results and the three-dimensional distribution of the Q-units in the bay indicate that the area has been affected by three abrasional/deposition cycles during the Late Pleistocene. During the earliest transgression the sea rose to a few metres above sea-level. During the second transgression it rose to −20 m. The last transgression took place when the sea rose to its present stand. While the sea stood at lowered levels, calcretes formed subaerially along ‘preferred’ zones in the marine deposits that were present. The main period of calcrete formation in the area was between the earliest and next transgression.