The Early Cretaceous Valley-floor Pene-Plain of the Lake Nyasa Region and its Relation to Tertiary Rift Structures

Abstract

On the floor of the upper Luangwa Valley of North-Eastern Rhodesia there are early Cretaceous Dinosaur Beds closely comparable with those occurring on the north-western floor of the Nyasa rift, and in recent papers (1937) I have given evidence to show that at least the northern ends of these two features, apart from the basin actually occupied by Lake Nyasa, had attained their present dimensions as far back as the early Cretaceous. Furthermore, having shown that the post-Karroo pebble beds of the upper Luangwa Valley belonged to the Dinosaur Beds, I suggested that the pebble beds of the lower Luangwa Valley were similarly assignable. On this and other grounds I suggested that the great system of troughs developed in this part of Africa, namely, those of the Luangwa and the middle and lower Zambezi, and the Nyasa-Shire rift, had attained to much of their present form in the early Cretaceous, and that the Dinosaur Beds and comparable formations filling these troughs had been base-levelled with the adjacent plateau during the Miocene peneplanation. Also, in a recent paper (1937c) on the early Cretaceous and Miocene peneplains of Nyasaland I described the secondary early Cretaceous peneplain on which rest the Dinosaur Beds and the Lupata series. I now adduce evidence to show that this secondary peneplain was an important feature in the early Cretaceous geology of this region, and that it extended as a great valley-floor surface of erosion, still recognizable, throughout the length of the system of troughs referred to. This