PALEOGEOGRAPHIC CONTROLS ON PALYGORSKITE OCCURRENCE IN MIDCRETACEOUS SEDIMENTS OF MOROCCO AND ADJACENT BASINS

Palygorskite has been identified as a major constituent of the clay fr action in mid-Cretaceous deposits of the Meseta, the Middle Atlas, and the Rif in central and northern Morocco. Two types of palygorskite ar e differentiated, based on the morphology of crystallites, bio- and li thofacies associations of the containing sediments. Type 1 occurs in s ections of the Meseta and the Middle Atlas, where the mineral displays bundles of long fibres under the electron microscope and is associate d with shallow marine carbonate and evaporite facies. Type 2 was found in the Rif, where palygorskite occurs mostly as bundles of shorter fi bres in turbiditic sediments of a supposed deep-marine environment. As sociated microfossils indicate reworking of the palygorskite-bearing s ediment from shallower parts of the basin. Palygorskite apparently gre w authigenically in the chemically restricted environments of the Mese ta and the Middle Atlas, whereas it is of a detrital origin in the Rif section. We consider that sediments containing authigenically formed palygorskite (type 1) could be the source of detrital palygorskite (ty pe 2). Type 1 deposits on the North African shelf were probably partly reworked and responsible for the supply of palygorskite to mid-Cretac eous Atlantic basins, where the mineral is well known from several DSD P sites. As in the case of various Recent deep-sea palygorskite occurr ences, aeolian transport may have significantly contributed to palygor skite supply to the ocean basins.