The structure of the external, fold-and-thrust region of the Neoproterozoic
Katangan orogenic belt of Central Africa is characterised by thrust sheets
, gravitationally transported towards the foreland region in the north, and
associated with prominent megabreccias. The thrust sheets contain a more o
r less complete succession of the Katangan sedimentary rocks. The megabrecc
ias form tabular and wedge-shaped, mostly chaotic bodies, underlying the al
lochthonous sheets and composed of subangular to rounded fragments of Katan
gan provenance. Fragments range from millimetres to many kilometres in size
and are set in an abundant clay matrix with dolomitic cement. It is common
ly accepted in the literature that the Katangan megabreccias are of entirel
y tectonic origin; friction acting beneath the advancing thrust sheets is t
hought to be the main process responsible for fragmentation and abrasion of
clasts. However, the analysis of stratigraphical, textural and structural
features presented in this paper implies a sedimentary genesis of the Katan
gan megabreccias. It is shown that they resulted from subaqueous re-sedimen
tation by mass gravity flows of clastic materials eroded from the emergent
tops and fronts of the advancing thrust sheets, in front of which olistostr
ome wedges were deposited. The deposition of each individual olistostrome b
ody stopped when the approaching thrust block overrode it due to the accele
ration of gravity gliding. These processes, and their products, define the
Katangan foreland region. The olistostrome sedimentary model has significan
t implications for our understanding of the structural and tectonostratigra
phic evolution of this sector of the Katangan belt. (C) 2000 Elsevier Scien
ce Limited. All rights reserved.