Mineralogía y génesis de las arcillas de la Unidad de Almarchal (series flysch del Campo de Gibraltar. S de España)

Abstract

A study of the fine fraction of the Almarchal unit (Campo de Gibraltar flysch series) revealed several very characteristic mineralogical associations, closely associated with the types of the rocks in this area.
1. Kaolinite-(illite)-swelling minerals, characteristically associated with the lutitic leves, clearly preponderate in this unit.
2. Illite-chlorite, a well-developed association found only in calcareous rocks.
3. Chlorite and/or berthierine, a characteristic association of silicified levels.
Thus, it is possible to determine a group of levels, typically turbiditic and another group of lutitic levels, probably hemipelagic deposits, in which the content of organic material is noteworthy. The control of the mineralogic evolution by lithology is a result of different permeabilities in alternating levels. In calcareous beds the mineralogy of the fine fraction could result from the diagenetic degradation of aluminosilicates. Diagenetic Fe-rich chlorites, preferably developed in siliceous rocks resulting from the evolution of detrital kaolinites. In lutitic beds, two types of mineral constituents are mixed: Typically detrital mineral species (like kaolinite) and diagenetic materials (swelling minerals). The abundance of organic matter in these levels can be related with oceanic anoxic events in Cretaceous time in North Atlantic basins.