Abstract: Calcite cements from the Lower Cretaceous Avalon zone of the Hibernia field are, in places, extensively recrystallized, which complicates interpretation of the chemical and isotopic data. The oxygen isotopic data are widely scattered with δ¹⁸O ranging between + 1.6 and −9.2 for calcite and siderite. Siderite has lower δ¹³C values (−6.6 to −13.2) than calcite +12.4 to −9.8. Typical trace element contents determined by ICP on acid-leached samples, range from 270 to 2100 ppm Sr and 180 to 2200 ppm Zn in calcite.

The trace element data indicate that some of the calcite has been precipitated from, or recrystallized by meteoric water. The trace elements show trends related to variations in δ¹⁸O in such a way as to imply that not all the spread to low δ¹⁸O values can be attributed to meteoric water influence alone. The data are not well enough constrained to calculate meaningful temperatures, but the range of °¹⁸O values probably represents an elevated range of temperatures of precipitation or recrystallization.

Microprobe analyses show that non-recrystallized fossils have a composition distinctly different from veins, cements, and recrystallized fossils, all of which are similar. The compositions of calcite cements are highly variable, with FeO (for example) ranging from 0.15 to 4.39 wt. %, but show no consistent patterns of zonation. Fossil fragments which show no textural evidence of recrystallization have low FeO contents (0.2 wt. %). Meteoric water, believed to be responsible for at least some of the cementation and recrystallization observed, probably entered the Avalon during and after formation of the mid-Cretaceous unconformity.