Formación de corrensita en turbiditas calcáreas con silex del Campo de Gibraltar (SW de España)

Abstract

In this paper is considered the relationship between the process of silicification in turbiditic limeslones and tbe growth of corrensite. This mineralogy is thought to be a result of two fundamental faetors: a) Type of detrital material, and b) Diagenetic conditions of the environment. Type of detrital material (in general similar to that found in otber calcareous rocks of the Campo de Gibraltar Units) determine tbe presence of illite and mixed-layers illite smectite, limited smectite and scarce kaolinite. Diagenetic environment is responsible for the corrensite and possible zeolite growth, and the carbonate silicification. The paragenesis and cbemical characteristics studied showed that the environment for the formation of these minerals needs a high activity of silica in solutions, a high content of iron (divalent) and magnesium, but is not necesarily be in relation with evaporitic deposits and thus alkaline conditions of formations. In this examples, the silicification process of limestone (which shows in the chemical analysis a certain proportion of iron and magnesium) is accompanied by iron oxides growth. The release of magnesium did not, as it frequently does, cause dolomite growth but, instead, led lo the corrensite formation. Because of the absence of siliceous organisms (radiolarian, sponge-spicules...) in this racles, the silicification process which has conduced lo development of chert nadules probably took place in an early stage of diagenesis, using silica precipitation from the solution. In this case, the volcanic activity cannot be considered as a last source of silica, as there is no evidence for contemporary volcanism with the sedimentation of these materials.