7 Sm-Nd Isotope Geochemistry of Argillaceous Sediments 189
were deposited directly on A.rchean crystalline basement. The fine-~ained pelites
and black shales alternate with sandstone, dolomite and ignimbrite tuff horizons.
Fig. 7.3. Mineralogy of the bituminous clay-shales from Gabon. A) Decrital, aligned
biotites. B) Authigenic clay minerals (illite. chlorite) in the clay matrix. C) Silicified and
decomposed alkali feldspars. D) Organic matter concentrated along the cIeavage planes of
the alkali feldspars E) Detrital alkali feldspar is replaced by the growth of fresh illite and
chionte (Stille eta[. 19931
were deposited directly on A.rchean crystalline basement. The fine-~ained pelites
and black shales alternate with sandstone, dolomite and ignimbrite tuff horizons.
Fig. 7.3. Mineralogy of the bituminous clay-shales from Gabon. A) Decrital, aligned
biotites. B) Authigenic clay minerals (illite. chlorite) in the clay matrix. C) Silicified and
decomposed alkali feldspars. D) Organic matter concentrated along the cIeavage planes of
the alkali feldspars E) Detrital alkali feldspar is replaced by the growth of fresh illite and
chionte (Stille eta[. 19931