Figure 5. Cross-Nichols photomicrographs of thin-sections from Late Oligocene volcaniclastic strata in the Margargaria River localities, northwestern Ethiopian Plateau.  5.1 A depositional unit matrix showing abundant concentrically-arranged iron-oxide nodules, where the main micro-feature is partial to complete coating by reddish iron-rich cement. Whitish material in interstitial spaces is chalcedony cement. CH-79-62TS. Scale bar equals 100 µm.  5.2 Angular plagioclase feldspar crystal sharply-rimmed by iron-rich cement from A depositional unit. CH-79-62TS. Scale bar 50 equals µm.  5.3 Angular hornblende crystal with its borders partially overgrown by reddish iron-rich cement from A depositional unit. CH-93-26TS. Scale bar 50 equals µm.  5.4 Cluster of small size angular pyroxene crystals partly coated by iron-rich cement from A depositional unit. CH-93-22TS. Scale bar 25 equals µm. 5.5 A depositional unit matrix showing opaque particles and disseminated bits of organic matter embedded in reddish iron-rich cement. CH-89-25TS. Scale bar equals 100 µm. 5.6 Massive to finely-laminated silt- and organic-rich B depositional unit matrix. Note abundant large angular volcanic rocks fragments and other angular to subangular rocks partly coated by iron-rich cement. CH-89-25TS. Scale bar equals 100 µm. 5.7 Approximately spherical bentonite bubbles in silt-rich B matrix. CH-89-24TS. Scale bar equals 50 µm. 5.8 Angular to subrounded intraformational clasts in B depositional unit matrix. CH-89-25TS. Scale bar equals 100 µm. 5.9 Concentrically-arranged iron-oxide nodules in B depositional unit matrix. Note rim of chalcedony cement surrounding the nodules. CH-89-24TS. Scale bar equals 100 µm. 5.10 Massive to faintly laminated silt-rich C depositional unit matrix. Note abundant angular elongate detrital glass shards and other volcanic rock fragments that delineate a "splintery" texture. CH-89-7TS. Scale bar equals 200 µm. 5.11 Angular elongate sanidine crystal from C depositional unit. CH-79-65TS. Scale bar equals 50 µm. 5.12 C depositional unit matrix showing numerous bentonite bubbles widespread in the matrix. CH-79-65TS. Scale bar equals 100 µm. 5.13 Single bentonite bubble from C depositional unit. Note rim of chalcedony cement and tiny crystal inclusion on the perimeter and inside bentonite bubble, respectively. CH-89-9TS. Scale bar equals 50 µm. 5.14 Massive to horizontally-microlaminated clay-rich D depositional unit matrix. Note abundant angular to subangular volcanic rock fragments, irregularly developed microscopic layers enriched in clay/organic content, and irregular to angular clasts of organic matter. CH-89-17TS. Scale bar equals 50 µm. 5.15 D depositional unit clay-rich matrix showing possible plant spores rimmed by chalcedony cement. CH-79-49TS. Scale bar equals 100 µm.