TY - JOUR AB - Vugs in lower Carboniferous limestone from Abercriban, southern Wales, are filled with calcite crystals displaying chemical growth zonation. Nine samples, physically separated from individual growth zones amalgamated from different crystals and analyzed by using standard acid digestion techniques, yielded ranges in δ 13 C and δ 18 O of +0.4‰ to -2.6‰ and -6.3‰ to -9.0‰, respectively. There is a general trend toward lighter carbon- and oxygen-isotope compositions in the younger zones. Thirty laser-ablation analyses of individual ~30-μm-wide zones from the same material revealed a much wider variation in δ 13 C and δ 18 O (+3.8‰ to -3.0‰ and -3.1‰ to -11.0‰), though with similar mean compositions. Significant jumps in isotopic composition were revealed between consecutive growth zones. The high spatial resolution of laser sampling has identified a fine-scale isotopic zonation that has hitherto gone undetected. This zonation suggests that calcite precipitation may be punctuated (or even driven) by changes in nature of pore water and sources of solutes. -from Authors AU - Dickson,JAD AU - Smalley,PC AU - Raheim,A AU - Stijfhoorn,DE DO - 10.1130/0091-7613(1990)018<0809:ICAOIV>2.3.CO;2 EP - 811 PY - 1990/// SN - 0091-7613 SP - 809 TI - Intracrystalline carbon and oxygen isotope variations in calcite revealed by laser microsampling T2 - Geology UR - http://dx.doi.org/10.1130/0091-7613(1990)018<0809:ICAOIV>2.3.CO;2 VL - 18 ER -