Organic matter-rich shale depositional environments

Abstract

Black shales are mixtures of terrigenous, biogenous, and hydrogenous sediment in which organic matter constitutes at least 0.5% of the material. Shales are the end product of the processes that control the production, erosion, transport, deposition, and diagenesis of mud. Although salt flocculation is an important mechanism, particularly in environments where water masses of different salinities mix, biogenic aggregation is probably the most important process controlling the behavior of mud in paralic and shallow marine environments. It is unsurprising that intervals of relatively widespread black shale deposition should coincide with eustatic highstands. Most ancient black shales appear to have been deposited in shallow marine epicontinental environments for which there are no modern analogs. Mud-dominated facies are the most abundant of all ancient shallow marine deposits. Black shales may be deposited in a wide range of sedimentary environments from the bottom of lakes to the abyssal plains of the ocean.