Die geologische Entwicklung von Süd-Mozambique seit der ...

seit der Unterkreide und die Ammoniten-Fauna usw. 261
Ncithcr morphology nor seismic and gravity data or magnetic anomalics in the
Mozambique Channel are typical of a spreading axis. Inclusions of sedimentary rocks
in the basaltic lavas of the Comores, geophysical and borcholc datas and outcrops on
either sidc of the channel assumed that the channcl is undcrlain by non-occanic crust.
This, and the stratigraphical-paleogcographical facts on both sides of the channel and
the first results of deep sea drilling suggest an unchanged position of Madagascar relative
to Africa since the late Paleozoic.
The geological history or Southern Mozambique and the Mozambique Channel
can at present be summarized as follows (Tab. 2, p. 138).
1. In late Paleozoic time there was uplifting of the Precambrian cratonic nuclei and
subsidcnce of the intracratonic bclts. Rifting occurred along the margins of the
cratons and parallel to the axes of the belts. Main activitv was in the south. In
troughs and graben-like structures the continencal Karroo sediments were deposited.
2. The first marine ingressions advanced on the eastern, Madagascian side in Permotriassic
time. The sea transgressed from north and south. The axis of the basin was
in the east close to Madagascar.
3. There was intensified uplifting and fissure-volcanism along the margins of the
cratons, limited to south and southeastern Africa. Igneous activity commenced in
late Triassic time with its maximum development in the south during late Triassic
to Lower Jurassic. This activity shifted to northeast during Jurassic and Cretaceous
times.
4. Invasion of the sea from the north and the south.
Transgression from the north: It is of Permotriassic age in northern Madagascar,
in the Mandera-Lugh and in the Mandawa basin. Toarcian in Somalia and northeastern
Kenya, northern and northwestern Madagascar. Upper Jurassic in northern
Mozambique.
Transgression from the south: Permotriassic in S outhern Madagascar. Bajocian in
western Madagascar. Early Upper Jurassic in Cape Province. South-Africa. Neocomian
in Zululand. Barremian in Southern Mozambique. Campanian in cen tral
Mozambique. The western Mozambique Channel was completely inundated by at
least mid-Cretaceous time.
5. Differential uplift with tiiting caused an easterly dip in southeastern Africa, and
a wcsterwnrd dip in western Madagaskar. Numerous marginal regressions and transgressions
occurred on both sides of the channel. There are maior unconformities in
southeastern Africa in Upper Ccnomanian to Turonian time, in Madagascar in
Santoiiian. Widespread igneous activity shifted from North ro South Madagascar
during the Turonian and Campanian time.
6. Maximum of the late Cretaceous transgression and extension of the sea took place
in Maestrichtian time. More shallow-watcr environments lollowed in Paleogene time
with a widespread regression in the Oligocene, possiblv with archipelago-like landbridges
between Mozambique and Madagascar tor a last migration of land animals.
7. A final transgression occurred in the early Miocene, followcd by a widespread regression
on both sides of the channel, probably in conncction with Cenozoic rifting in
Hast Alrica. The centre of activity shifted northwarcls with time from Tair/ania to
l-'thiopia. There was no Pleistocene voleanism in southeastern Alrica, but widespread
igneous activity in the Mozambique Channel and in central and eastern Madagascar.