Publication: Grain size, composition, porosity and permeability contrasts within cross-bedded
sandstones in Tertiary fluvial deposits, central Spain
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Publication Date
1993
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Blackwell Publishing Ltd
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Abstract
Permeability measured with a portable probe pcrmcflmeter on outcrops of cross·bcdded sandstones ranges
betwecn 0·9 and 19 O. The highest pcrmeability (2-19 0 with an avcrage of8·5 D) occurs in thc coarsest
grained foresct laminae (CFL). intermediate values (2-120 with an average of 5·3 D) occur in fincr
grained foreset laminac (FFL) and thc lowest values (0·9-1 0 0 with un avcrage of 4·8 D) occur in boltomsct
laycrs (BL). In the cross·bcds the uverage grain sizc rangcs from medium graincd sand in the CFL to finc
grained s,lnd in thc FFL and BL. In all three subf'lcies. the average size of the primary pores is
approximately It/> unit smaller than the averagc grain size. The abundance of unstablc carbonatc clasts
correlatcs with incrcasing avcrage grain size, micritic clasts being most abundant in the CFL. Converscly.
quartz content incrcascs with decreasing grain size and is highest in the FFL and BL. Oiagenetic
destruction of primary porosity by compact ion and cementation. as well �IS generation of sccondary porosity
through dissolution, were controlled by the original mineralogical composition of the sand. Contrasts in
grain size detcrmine the primary pore size contrasts and differences in composition bctwecn CFL. FFL
and BL. Permeability contrasts reflect variations in averagc primary pore size rather than differenccs in
total porosity. Probe permeability contrasts between eFL. FFL and BL depend on contrasts in llverage
pore size and contrasts in mineralogical composition between the subfacies.
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