Geochemical History of Calcite Precipitation in Tertiary Sandstones, Northern Apennines, Italy
- 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
Milliken, K. L., McBride, E. F., Cavazza, W., Cibin, U., Fontana, D., Picard, M. D. and Zuffa, G. G. (1998) Geochemical History of Calcite Precipitation in Tertiary Sandstones, Northern Apennines, Italy, in Carbonate Cementation in Sandstones: Distribution Patterns and Geochemical Evolution (ed S. Morad), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304893.ch10
- Published Online: 17 APR 2009
- Published Print: 29 MAY 1998
Print ISBN: 9780632047772
Online ISBN: 9781444304893
- geochemical history of calcite precipitation in tertiary sandstones in northern Apennines, Italy;
- ten tertiary stratigraphical units;
- sampling and methods;
- acid soluble carbonate in mudrock;
- detrital and authigenic carbonate in sandstones
In order to better understand the origin and controls of calcite cementation in marine sandstone we studied ten Tertiary lithostratigraphical units exposed in the northern Apennines, Italy, which display a variety of patterns of calcite cement. Five of the units studied were deposited in piggy-back (satellite) basins, and five were deposited in foreland basins. Burial depths of cemented units in piggy-back basins range from 0 to 1300 m, whereas burial depths of foreland basin rocks range from 500 to >7000 m.
Petrographic data and stable isotopes indicate that detrital carbonate particles (rock fragments and marine skeletal debris) in both sandstones and intercalated mudrocks were the main sources of calcium and carbon in cement. Cementation took place at or near maximum burial depth in most of the shallowly buried units, and at somewhat less than the maximum burial depth for the deeply buried units. Oxygen isotopes indicate that (i) the Intra-Apenninic Pliocene, Antognola and Ranzano stratigraphical units were cemented by fluids with negative δ18O values (i.e. deeply circulated meteoric water from nearby mountains); (ii) the Bismantova, Borello and Loiano formations were cemented by water with a meteoric component; (iii) all the foreland basin units contain calcites with δ18O that is permissive of fluids that ranged from slightly negative to markedly positive (−2 to +7‰). δ18O-enriched values of δ18Owater are compatible with plausible depths and temperatures of cementation of the three deepest formations, where water evolved from silicate reactions dominated, but not for the less deeply buried ones. Possible replacement of earlier-formed calcite by higher-temperature material cannot be ruled out for the deepest-buried formations.
Multiple samples taken from concretions vary less than 2‰ (and commonly less than 1‰) in δ13C and δ18O from core to margin, without any consistent trend. In contrast, variations in isotopic values between concretions in the same formation are greater: oxygen isotopes commonly differ by 4‰ (locally greater) within a single formation. A combination of variations in temperature and water composition seems to be the cause. In the Loiano Formation there is a significant difference between δ18O values of bedding-parallel concretions and fault-parallel concretions, which reflects different times of cementation.
Variations in Mg, Fe, and Mn concentrations reflect zoning in some of the concretion calcites examined. Covariations between these minor and trace elements differ greatly both between formations and between samples within a single formation. From limited temporal information it appears that the availability of Mg and Fe was greatest relatively early in diagnesis, whereas Mn was mobilized in at least two distinct pulses, one early and one late.
Burial depth and its attendant temperature played a more important role in diagenesis than whether a formation was deposited in a piggy-back or a foreland basin.