Origin of Low-Permeability Calcite-Cemented Lenses in Shallow Marine Sandstones and CaCO3 Cementation Mechanisms: An Example from the Lower Jurassic Luxemburg Sandstone, Luxemburg
- Sadoon Morad
Published Online: 17 APR 2009
Copyright © 1998 The International Association of Sedimentologists
Carbonate Cementation in Sandstones: Distribution Patterns and Geochemical Evolution
How to Cite
Molenaar, N. (1998) Origin of Low-Permeability Calcite-Cemented Lenses in Shallow Marine Sandstones and CaCO3 Cementation Mechanisms: An Example from the Lower Jurassic Luxemburg Sandstone, Luxemburg, in Carbonate Cementation in Sandstones: Distribution Patterns and Geochemical Evolution (ed S. Morad), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304893.ch9
- Published Online: 17 APR 2009
- Published Print: 29 MAY 1998
Print ISBN: 9780632047772
Online ISBN: 9781444304893
- low-permeability calcite-cemented lenses in shallow marine sandstones;
- calcite cemented layers and lensoid concretions;
- carbon isotopic composition of calcite;
- late calcite cementation mechanism;
- differential early calcium carbonate cementation
Calcite-cemented layers and lensoid concretions commonly form low-permeability barriers in shallow marine reservoir sandstones. In the porous and permeable Lower Jurassic Luxemburg Sandstone such calcite-cemented lenses form permeability barriers with lateral continuities of a few decimetres to hundreds of metres. Deposition of these sandstones (≤90 m thick) occurred in a wave- and storm-reworked tidal delta that formed where a seaway through the Ardennes and Rhenish Massifs entered the shallow Paris basin.
The main cause of tightly cemented layers and lenses is differential early marine calcite/aragonite cementation. Early cementation took place a few decimetres below the sea floor within the uppermost sediment layers, where cementing materials were supplied by sea water flowing through the sand. Occasionally, early lithified layers were exposed at the sea floor after erosion, and typical hardground features such as borings and encrustations of fauna developed. Precipitation of early marine cement was controlled by the carbonate grain content and texture of the sand. Cementation began in permeable structures of the sand which had elevated carbonate grain content. The intensity of early cementation and the eventual lateral extent of cemented layers were dependent on sedimentation rate as a function of intermittent storm deposition and reworking. Early diagenesis and the distribution of calcite-cemented lenses are thus controlled by sedimentary facies.
The local presence of early cement decreased permeability and constrained the flow of pore water and later diagenetic processes such as dissolution or replacement of carbonate grains and poikilotopic or blocky calcite cementation, demonstrating their dependence on hydraulic flow. Dissolution of carbonate grains caused the development of extensive secondary porosity in the host rock. Replacement of metastable frameworks and early diagenetic carbonates by calcite and sparry calcite cementation took place almost exclusively in the early calcite-cemented lenses. As a result, the initial differences in detrital mineralogy and early diagenesis of lenses and host rocks were further enhanced during later diagenesis.