The limited abundance of dolomite in Cenozoic and modern marine environments, in contrast to its prevalence in older Phanerozoic strata, remains a long-standing enigma in sedimentary geology. This disparity has been linked to kinetic barriers that inhibit dolomite precipitation under present-day marine conditions or, alternatively, to the insufficient thermal maturation of younger carbonate platforms, preventing dolomitization during burial.
To address this issue, we analyzed δ¹³C, δ¹⁸O, and TΔ47 values in carbonate samples from the Albian Reef complex at Nahal Me’arot, northern Israel. Our results indicate that massive replacive dolomites are confined to the back-reef lagoon facies and formed through reflux-brine dolomitization at shallow burial depths. These dolomites exhibit a negative correlation between TΔ47 (29-54°C) and δ¹⁸Odolomite (-3.25 to -1.35 ‰VPDB), suggesting recrystallization under burial conditions (reaching depths up to 1-2 km) in the presence of seawater-derived pore fluids (δ¹⁸Owater = -1‰VSMOW). In contrast, limestone samples from the fore-reef and reef core recorded lower δ¹⁸Ocalcite (-4.4 to -5.5 ‰VPDB) and higher TΔ47 values (45-121°C), consistent with diagenetic alteration at greater depths. U-Pb dates of those samples are significantly younger than the stratigraphic age of rocks, consistent with clumped isotope data, indicating that both methods record late-stage diagenetic alteration.
These findings support a two-stage model for dolomitization: (1) initial formation of Mg-enriched proto-dolomite in shallow depositional environments influenced by brine reflux, followed by (2) later recrystallization of proto-dolomite under increased burial temperatures. Compilations of Mg/Ca ratios in Cenozoic marine carbonates predict more dolomite than is observed directly, suggesting that the lack of thermal maturity has been a limiting factor for dolomite occurrence in Cenozoic strata.