Figure F20. Comparison of Rock-Eval pyrolysis hydrogen index and Tmax values for black shale and underlying claystone units of the five sites cored during Leg 207 on Demerara Rise. Fields for Type I (waxy), Type II (algal microbial), and Type III (land plant/detrital) organic matter are shown. Compositions of the black shales are dominated by thermally immature, relatively well preserved algal-microbial organic matter.