High-resolution carbonate isotopic study of the Mural Formation (Cerro Pimas section), Sonora, Mexico: Implications for early Albian oceanic anoxic events

摘要

The 420-m thick stratigraphic section of the Mural Formation that is exposed in the Cerro Pimas area of northern Sonora, Mexico, is composed of limestone lithofacies ranging from bioclastic wackestone to boundstone, whose biota is characterized by low diversity. Prominent age-diagnostic fossils are benthic foraminifera and long-ranging calcareous algae that indicate the Aptian/Albian boundary is close to the base of the Los Coyotes Member. The carbonates of this formation have negative to positive delta C-13 values (-4.63 to +2.6 parts per thousand) and highly depleted delta O-18 values that range from -12.74 to -8.34 parts per thousand. The absence of correlation between delta C-13 and delta O-18 values supports a primary marine origin for the delta C-13 values of these limestones.