Many black shales in thick epicontinental basinal successions formed beneath an oxygen restricted "puddle" of deep water. Other black shales formed during rapid transgression when basinal deposition expanded to cover basin-margin areas normally characterized by shallow-water deposition. An "expanding-puddle" model is developed from the Early Jurassic of England wherein rapid sea-level rise leads to marine-sediment starvation due to sediment entrapment in flooded river valleys. Subsidence, sea-level rise, and decreased sediment supply during early transgression are suggested to lead to rapid deepening and therefore the expansion of the area of the "puddle" such that, in previously shallow-water areas, black shales rest on condensed basal transgressive lags or unconformities that in turn rest on shallow-water facies. Reestablishment of sediment influx and aggradation in excess of any continued sea-level rise cause shallowing throughout the basin and the cessation of black-shale formation.

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