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Fig. 12-11. Regional contour map of base Upper Cretaceous sedimentary rocks in the east
Sirte basin (contours in feet). The line of the cross-section of Fig. 13-1 passes through In-
tisar and the southern margin of Augila. (Adapted from Williams, 1972, p. 625, fig. 2, and
Brady et al., 1980, p. 544, fig. 1.)

banks up to 200 m thick. The second transgressive pulse motivated the growth
of coral reefs, and their ultimate extermination.
Terry and Williams also report that the coral reef member of the bioherm
has two mappable units - a coralline biomicrite overlain in general by reef
limestone. The coralline biomicrite forms a lens-like body that thins to the
edges of the reef from 90 to 105 m in the centre. It has about 15% porosity,
but low permeability because much of the porosity is due to solution of coral
skeletons and is not effective porosity. The reef limestone is 100-150 m
thick. Detrital biomicrite both in coral chambers and coral framework in-
dicates that the corals had a capacity to retain sediment. The porosity of this
unit is intergranular and averages about 22%. The reef is overlain by a dense
biomicrite, overlain in its turn by the Upper Kheir marl.