Figure 6. Cross-Nichols photomicrographs of thin-sections from Late Oligocene volcaniclastic strata in the Margargaria River localities, northwestern Ethiopian Plateau. 6.1 D depositional unit matrix showing abundant subangular to subcircular masses of volcanic rock fragments and intraformational clasts. Note larger spherical intraformational clast (right side of image) formed by claystone, organic matter, and volcanic rock fragments and rimmed by chalcedony cement. CH-79-57. Scale bar equals 115 µm. 6.2 Microlaminated to massive, clay-rich, E depositional unit matrix. Note volcanic rock fragments, feldspar crystals (whitish angular particles), and abundant microlenses (~micro mud drapes) of organic matter in matrix. CH-79-45. Scale bar equals 140 µm. 6.3 Subrounded organic clast (possible plant spore) in E depositional unit matrix. CH-79-45. Scale bar equals 50 µm. 6.4 Subrounded organic clast (possible root fragment) in E depositional unit. CH-93-12. Scale bar equals 50 µm. 6.5 Angular volcanic rock fragments and feldspar crystal (larger fragment on left of image) in clayey E depositional unit matrix. Note reddish iron-rich cement coating rocks and crystal. CH-79-45. Scale bar equals 50 µm. 6.6 Massive to weakly-laminated clay- and organic-rich F depositional unit matrix. CH-79-45. Scale bar equals 200 µm. 6.7 Microscopic lens/pocket of organic-rich material in F depositional unit matrix. CH-79-44. Scale bar equals 100 µm. 6.8 Possible plant spore in F depositional unit matrix. CH-79-63. Scale bar equals 50 µm. 6.9 Roots cross to oblique sections in F depositional unit matrix. Note dark-reddish iron-rich cement bordering roots. CH-89-26. Scale bar equals 50 µm. 6.10 Blocky siderite crystal in F depositional unit matrix. CH-79-44. Scale bar equals 50 µm. 6.11 Coarsely to finely-laminated organic-rich G depositional unit matrix. Note laminated structure represented by undulating and convoluted layers not firmly appressed to each other. CH-89-13. Scale bar equals 100 µm. 6.12 Small rounded volcanic rock fragments in free spaces between organic layers of the G depositional unit matrix. CH-89-13. Scale bar equals 50 µm.