Abstract

Characterization of Devonian-Mississippian black shales in central and eastern Kentucky shows that cyclicity involving alternating black and grey shales in eastern Kentucky is also apparent in the thinner, coeval, homogeneous black shales of east-central and central Kentucky through alternation of transgressive and regressive black shales. These cyclic transgressive-regressive continua apparently relate to pulses of tectonism and quiescence in the Acadian orogen. Organic-rich black shales in each cycle are called transgressive black shales and reflect regional subsidence and transgression accompanying tectonism. Grey shales in each cycle are distal parts of clastic progradations during intervening periods of tectonic quiescence and resulting cratonic relaxation and upwarping; locally, this upwarping was apparently responsible for maintenance of dysaerobic conditions in distal areas. The grey shales, however, eventually grade into silty black shales, called regressive black shales because of their equivalence to clastic wedges.

Transitions from grey to black shales mark former positions of pycnoclines in stratified water columns. We suggest that changes in the positions of paleopycnoclines during black-shale deposition in Kentucky reflect migration of foreland basins and peripheral bulges associated with deformational loading in the orogen. Acadian and probably other coeval tectonism on the craton seems to have influenced black-shale deposition, but the larger effects have been obscured locally in Kentucky by concurrent eustacy or synsedimentary structural activity.