Origin, distribution and significance of carbonate cements in the Albert Formation Reservoir sandstones, New Brunswick, Canada

Carbonate cements in the fluvio-lacustrine reservoir sandstones of the Albert Formation mainly occur in three phases: pre-compaction calcite, post-compaction calcite and ankerite. The precompaction calcite cement (25% to 40%) is characterised by bright luminescence, high concentrations of Fe, Mn and Sr(means of 1.56 wt.%, 1.42 wt.% and 0.25 wt.%, respectively), slightly heavy delta(13)C and delta(18)O values (mean = -1.79 parts per thousand PDB, mean = -14.99 parts per thousand PDB, respectively), and its selective occurrence in lacustrine sandstones suggestive of cementation at shallow depths from lacustrine connate water. Dull-luminescence, variable concentrations of Fe, Mn and Sr, variable but slightly heavy delta(13)C and delta(18)O values (mean of -2.97 parts per thousand PDB, and -11.05 parts per thousand PDB, respectively) of the post-compaction calcite, as well as its occurrence in alluvial fan sandstones exhibiting high pressure solution of detrital grains, suggest cementation from pore waters modified by water-rock interactions. We suggest that the ankerite cement was formed from upwardly migrating formation water based on the following evidence: (i) ankerite cement filling the secondary pores created in the deep subsurface, (ii) an absence of unconformity during ankerite cementation precluding involvement of meteoric water, (iii) ankerite cementation in brecciated veins synchronous with ankerite precipitation in host sandstones, (iv) occurrences of significant volumes of ankerite (20% to 30%) in the shales indicating that the Fe and Mg ions expelled during smectite to illite transformation reactions were consumed within the shales, and (v) the heavy delta(13)C and delta(18)O isotope values of the ankerite cements (means of +2.20 parts per thousand PDB and -11.05 parts per thousand PDB, respectively). Copyright (C) 1996 Elsevier Science Ltd