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

2 5 S R . F ö r s t t r . D ie geologische U m w icklung von SiUl-M ozaniliique
castwards of the Mabote-Fuiihalouro Rift, part of the East African Rift systcm. The
present investigations are based upon fieldwork carricd out in 1967, 1969 and 1971 in a
Programme sponsored by the Deutsche Forschungsgemeinschaft.
The Mozambique Plain torms a part of one of the large Mesozoic Cenozoic sedimentary
basins along the East African coast, ranging from the basin of Somalia in the
north to the Agulhas Plateau in the south. 1t is boundcd by three cratons, already Consolidated
in Precambrian and late Caledonian time: the Mozambique Belt in the north,
the Rhodesian craton in the west, and the Kaapvaal eraton in the soutlnvest. Betvveen
these old cratons there were arranged two intracratonic belts, striking more or less
West— East: the Zambezi Belt and the Limpopo Belt. These belts started as intracontinental
troughs in Palcozoic time, accumulating the Continental detritus of the
Karroo formation. With the breakup of the Gondwana continent, the igneous activity
of the late Karroo was lined up along fissurcs parallel to the axis of the troughs and
along the margins of the old cratons. Between Karroo volcanism and the Crctaceous
transgression there was a period in which the subcontinent was subjected to differential
uplift and erosion.
Barre mian and Aptian
The sea reached Southern Mozambique in Lower C rctaceous time from the southeast
and transgressed over deeply wcathered Karroo-basalts with a slight angular unconformity.
Nodules in fine-grained glauconitic sandstones 3— t m above the basal conglomerate
yielded a sparsc fauna of Barremian age. From the late Aptian to the
Lower Cenomanian there was no change in S e d im en tatio n : glauconitic fine-grained
sandstones and sandy marls with occasional layers of nodules or sandy limestones. The
uppermost Aptian (Clansayesian) is represented by faunas with a close relationship to
Madagascar and Southern Russia. Increasing numbers of pebbles, conglomerates and
thickshelled bivalves o f a Coastal to beach environment indicate a proceeding regression
in the uppermost Aptian.
A 1 b i a n
Lower Albian is not vet recorded. Donvilleiccras cf. mammillatum (Schlotheim)
proves the presence of Middle Albian. The sediments resenible those of the Aptian,
consisting of about 300 m of glauconitic silty sandstones with rare intercalations of
thin layers of sandy limestones. Nodules yielded rieh faunas of a shallow-water environment.
In the late Albian another regression followed. Bcds with pebbles and
layers of conglomerates characterize the uppermost Albian. The local occurrence of
these coarser detritus only in a restricted area along the Maputo River, the rapid
decrease northwards and the relatively high percentage (more than 2%) of Precambrian
pebbles point to an old drainage systcm, rcaching far into the hinterland. While in the
deeper parts of the basin the Sedimentation seems to have cominucd without a break
from Albian to Cenomanian, uppermost Albian and the lowcst Cenomanian are absent
in the marginal parts of the basin and farther to the north, ln the region of the Maputo
River, the sequence of Barremian to Lower Cenomanian strata may attain a thickncss
of about 50C—600 m. Only 60 km northwards, along the Mahube River, the thickness
is down to 60—90 m without a trace of Barremian, Aptian and Lower Albian. Near
Boanc Continental sandstones lie on Karroo basalts; in the Incomati River area 170 km
north of the Maputo River only transgressive Campanian and Maestrichtian sedi­