Carbonate Cementation in Tertiary Sandstones, San Joaquin Basin, California
- 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
Boles, J. R. (1998) Carbonate Cementation in Tertiary Sandstones, San Joaquin Basin, California, in Carbonate Cementation in Sandstones: Distribution Patterns and Geochemical Evolution (ed S. Morad), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304893.ch12
- Published Online: 17 APR 2009
- Published Print: 29 MAY 1998
Print ISBN: 9780632047772
Online ISBN: 9781444304893
- carbonate cementation in tertiary sandstones, San Joaquin basin, California;
- San Joaquin basin, California;
- basin pore water;
- timing of cementation;
- diagenetic history of basin;
- basin centre cements
Carbonate-cemented sandstones occur throughout the San Joaquin basin. New isotopic data from nine additional areas combined with published papers allow comparison of cement compositions throughout the basin and a quantitative model of cement timing.
In marine turbidite sandstones of the central basin, following minor siderite precipitation, dolomites formed early in the zone of methanogenesis. These have Ca-rich compositions similar to dolomites reported from contemporaneous fine-grained rocks of the Monterey Formation, coastal California. The dolomites are an example of young (< 6 Ma) dolomite formation at shallow burial depth in marine pore water, and they may have undergone some recrystallization during shallow burial without resetting their initial 87Sr/86Sr values.
Calcite cements in the central basin formed between burial depths of about 1.5 km and > 4 km. The calcites show significantly lower 87Sr/86Sr values than the depositional marine water, and have progressively lower ratios with increasing burial depth. The latest cements have 87Sr/86Sr ratios lower than any possible marine pore water, and the ratios indicate that Sr and Ca are sourced from plagioclase feldspar. Calcite cements formed at intermediate burial depths have carbon isotopic compositions sourced in part from thermogenic-derived carbon but during deep burial, carbon isotopic values near zero (PDB) suggest carbon derived from unknown reactions, possibly related to the organic acids in the oil reservoir. Sr isotopic values preclude dissolution of shell tests as the primary carbon source in these late calcites. Late cements appear to have formed in a relatively closed system, on the reservoir scale, during the dissolution of detrital plagioclase within the reservoirs, possibly during hydrocarbon emplacement.
The basin margins are characterized by calcite and minor dolomite cements, many of which which formed in isotopically light brackish or meteoric water at low temperature. In general, calcites did not form near the sediment-water interface, but during shallow burial. On the east side of the basin these cements are characterized by widely varying δ13CPDB values (+20 to −30) compared with central basin cements (+5 to −10). Sr isotopic ratios in cements are lower than the marine depositional waters on the east side of the basin, but are higher than expected for depositional waters on the west side.
Although the San Joaquin basin has evidence for cross-formational fluid flow, in many cases each reservoir has carbonate cements with distinctive compositions. This indicates that the flow that has occurred has not been at a rate or magnitude sufficient to homogenize the pore fluids within closely spaced reservoirs.