J. Bertrandsarfati et B. Potin, MICROFOSSILIFEROUS CHERTY STROMATOLITES IN THE 2000 MA FRANCEVILLE GROUP, GABON, Precambrian research, 65(1-4), 1994, pp. 341-356
Cherty stromatolites, reported here for the first time, have been foun
d in the Palaeoproterozoic (2000 Ma) cover of the Chaillu craton in Ga
bon. They occur in two different areas, probably in the same formation
(FC), which comprises widespread beds of black shales and silexites.
The buildups are 1-2 m thick biostromes comprising juxtaposed domes of
pseudo-columnar to columnar stromatolites. The biostromes are transgr
essive over topographic highs marginal to the Francevillian basins. Th
e environment was a protected shallow-marine area with occasional inpu
ts of small quantities of peloidal sediment deposited between the colu
mns. The high organic carbon content of Francevillian formations FB, F
C and FD allows us to consider them as source rocks for the bitumen no
w found in the FA sandstones. The stromatolites and their preserved mi
crofossils support the hypothesis that microbial activity was at the o
rigin of bitumen production.