Orbital forced cyclicity of reflector strength in the seismic records of the Cape basin

Abstract

A well-pronounced succession of continuous high-amplitude reflectors characterises the upper acoustic units off Southwest Africa as revealed in our seismostratigraphic study. We performed spectral analyses over age-transformed seismic traces. The results suggest a temporal regularity in the variation of reflector strength according to Milankovitch cycles since the early Pliocene. Periods of 100 kyr/cycle between 0-2 Ma correspond to eccentricity modulations. From 2-3 Ma, shorter periods close to obliquity cycles prevail, whereas in even older units periodicity increases again to 100 kyr/cycle. We propose the cyclicity of high-amplitude reflectors is caused by orbitally driven climate variations, which modulate the sedimentary properties and with it the seismic reflectivity. Copyright 2007 by the American Geophysical Union.