Abstract

Mr. J. W. Pallister commented on the distinct submarine canyon off the mouth of the Orange River depicted on the slide illustrating the base of the Tertiary formations on the shelf. He contrasted this feature with the much less defined canyon in the mid-Tertiary surface where a distinct delta-fan appears and increases in the Holocene. He enquired whether this change can be matched by any special features of the Orange River valley and its regime during the period. Had the author been able to correlate the offshore erosion and deposition features with changes in the Orange River erosion history ?

The Author replied that he was not sure which figure Mr. Pallister referred to as an illustration of “the base of the Tertiary Formations on the shelf,” as no data are available with which to construct such a map. Penetration to the top of the Mesozoic was not achieved beyond a few miles from shore, and the only data on the depth to the base of the Tertiary are from the one line of refraction sites to which reference is made in the text and on the seismic profiles. A valley across the shelf seems to have been cut by the Orange River during the mid-Tertiary regression and the bulk of Neogene and Holocene sediments certainly originated from the Orange River, although the rate of accumulation appears to have been much slower than during earlier periods. Reference to the role of the Orange River is made in reply to Dr.

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