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ABSTRACT

Sedimentary ball structures observed in the Visean series of Jebel Tekzim, in the Palaeozoic massif of the eastern Jebilet Range, Morocco, are described and interpreted.

The metre-sized balls are composed of carbonate. They are texturally akin to wackestone or packstone, and some display a spiralled internal organization. The balls are encased in a calcarenitic to conglomeratic matrix and directly overlie a shale unit.

The origin of the structures is thought to be analogous to the mechanism whereby an avalanche of wet snow gives rise to the deposition of snowballs at the base of a slope. A layer of carbonate sediment detaches along an organic-rich horizon and rolls up during downslope movement under gravity.