Condiciones de formación de Paligorskita-Sepiolita en litofacies dolomíticas de la cubeta de Piedrabuena. Campo de Calatrava (Ciudad Real)

Abstract

Mineralogical, textural and chemical features of two drilling cores that cross over dolomite marls and green clays from Piedrabuena basin (Campo de Calatrava, Central Spain), are studied. The experimental results let us to stablish three stages showing a shallow lacustrine environment with climatic and tectonic changes:
a) Lower stage (drying). Massive dolomicrites with increasing- desiccation features at topo Mineralogical association: dolomite-phyllosilicates (sepiolite-palygorskite-illite).
b) Middle stage (expansive-retractive). Dolomicrites and intradolomicrites, sometimes bearing clasts, with early dedolomitization textures. Mineralogical association: dolomite-phyllosilicates (palygorskite-sepiolite-illite-dioctahedral smectite)-calcite-quartz.
c) Upper stage (freshening). Dolomicrites witb calcite related to dedolomitization processes and thin clay layers witb clasts (quartz, quartzite, mica and carbonates). Mineralogical association: dolomite-ealcite-phyllosilicates (palygorskite-illite-dioctahedral smectite-kaolinite)-quartz.
Illite, dioctahedral smectite and kaolinite show a clearly detrital origin from surrounding materials (Palaeozoic quartzites and slates), whilst palygorskite and sepiolite origin is related with early diagenetic processes. So, sepiolite in dolomicrites is associated to desiccation conditions and palygorskite seems have been Cormed after alteration of precursor phases, dioctahedral smectite mainly, under floods conditions. Moreover, both sepiolite and palygorskite show a relation among their genesis, amorpbous silica contents (up to 5.5%), and dedolomitization processes, in a Mgrich environmenl.