Publication: Giant calcite concretions in aeolian dune sandstones; sedimentological and
architectural controls on diagenetic heterogeneity, mid-Cretaceous Iberian
Desert System, Spain
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Publication Date
2012
Authors
Meléndez Hevia, Nieves
Soria de Miguel, Ana Rosa
De Boer, Poppe
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Elsevier B.V.
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Abstract
Aeolian dune sandstones of the Iberian erg system (Cretaceous, Spain) host giant calcite concretions that constitute
heterogeneities of diagenetic origin within a potential aeolian reservoir. The giant calcite concretions
developed in large-scale aeolian dune foresets, at the transition between aeolian dune toeset and damp interdune
elements, and in medium-scale superimposed aeolian dune sets. The chemical composition of the giant
concretions is very homogeneous. They formed during early burial by lowMg-calcite precipitation frommeteoric
pore waters. Carbonate componentswith yellow/orange luminescence form the nuclei of the poikilotopic calcite
cement. These cements postdate earlier diagenetic features, characterized by earlymechanical compaction,
Fe-oxide cements and clay rims around windblown quartz grains resulting from the redistribution of aeolian
dust over the grain surfaces. The intergranular volume (IGV) in friable aeolian sandstone ranges from 7.3 to
15.3%, whereas in cemented aeolian sandstone it is 18.6 to 25.3%. The giant-calcite concretions developed during
early diagenesis under the influence of meteoric waters associated with the groundwater flow of the desert
basin, although local (e.g. activity of fluid flow through extensional faults) and/or other regional controls
(e.g. variations of the phreatic level associated with a variable water influx to the erg system and varying
sea level) could have favoured the local development of giant-calcite concretions. The spatial distribution
pattern of carbonate grains and the main bounding surfaces determined the spatial distribution of the concretions.
In particular, the geometry of the giant calcite concretions is closely associated with main bounding
aeolian surfaces. Thus, interdune, superimposition and reactivation surfaces exerted a control on the concretion
geometries ranging fromflat and tabular ones (e.g. bounded by interdunes) towedge-shaped concretions at the
dune foresets (e.g. bounded by superimposition and reactivation surfaces) determining the spatial distribution of
the heterogeneities of diagenetic origin in the aeolian reservoir.