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Lacustrine chalky carbonates: origin, physical properties and diagenesis (Palaeogene of the Madrid Basin, Spain)

Arribas Mocoroa, María Eugenia and Bustillo Revuelta, María Ángeles and Tsige Aga, Meaza (2006) Lacustrine chalky carbonates: origin, physical properties and diagenesis (Palaeogene of the Madrid Basin, Spain). Sedimentary Geology, 166 . pp. 335-351. ISSN 0037-0738

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Abstract

The Palaeogene lacustrine chalky carbonates of the Madrid Basin are a peculiar type of very soft and friable carbonate
facies with high porosity despite being covered by more than 800 m of sediment. Similar physical properties to those
described in marine chalk reservoirs emphasize the interest in analysing and characterizing these carbonate facies within a
lacustrine depositional system. Lithologically, they are calcitic and/or dolomitic poorly cemented carbonate muds with no
significant amounts of skeletal debris. Clay minerals such as illite, smectite and palygorskite are present between the carbonate
crystals. Palygorskite is the most common, covering the carbonate crystals and forming sheets between them. These lacustrine
chalky carbonates were formed in the basinal areas of the lake as the result of inorganic carbonate precipitation and/or detrital
sedimentation related to episodic reactivation of the adjacent fan systems. Their petrological, geochemical and physical
properties indicate that few textural and compositional modifications occurred during diagenesis. Their main physical
properties are a very low dry bulk and grain density (1.6–2.2 and 2.62 g/cm3, respectively) and medium to high porosity (10–
40%) due to micropores ( < 2 Am, 70%) and macropores (>2 Am, 30%). The convergence of lacustrine sedimentation
dynamics (rapid sedimentation), the original mineralogy of these calcareous lacustrine muds (relatively stable low-magnesian
calcite and dolomite), the early formation of the palygorskite cement of these muds, and the retention of Mg-enriched fluids in
the pore system, were decisive in the partial inhibition of calcite cementation, compaction and recrystallization. The chalky
carbonates are also intercalated between impermeable littoral carbonate facies that impeded fluid flow through their pore
systems.


Item Type:Article
Uncontrolled Keywords:Chalky carbonates; Lacustrine deposits; Physical properties; Overpressure; Palygorskite; Palaeogene
Subjects:Sciences > Geology > Petrology
ID Code:17289
Deposited On:30 Nov 2012 11:59
Last Modified:16 May 2013 11:20

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