In each Upper Carboniferous cyclothem, offshore shale is overlain directly by __________ as a result of __________.

Question

Quizplus · Accepted Answer

The Upper Carboniferous cyclothem is characterized by an alternating pattern of marine and non-marine sedimentary rocks. Each cyclothem typically begins with offshore shale, which is then overlain by limestone as a result of transgression (sea-level rise). The limestone can sometimes be replaced by coal if the area experienced prolonged non-deposition or peat accumulation. Therefore, option A is incorrect as coal is not always present. Underclay, which is a layer of clay formed from the roots of plants, forms under coal and is not directly overlain on offshore shale. Option B is therefore incorrect. Option D is incorrect because nearshore sandy shale is not typically found directly above offshore shale in a cyclothem.

In Each Upper Carboniferous Cyclothem, Offshore Shale Is Overlain Directly