Carbonate Cycle Stacking Patterns and Hierarchies of Orbitally Forced Eustatic Sealevel Change

Abstract

Ordered stacking of meter-scale upward-shallowing cycles, manifested as repeated thickness hierarchies within cratonic carbonate sequences, has been considered primary evidence for causal relations between orbitally forced climate change and eustatic sealevel variation. Explicit in this argument is the assumption that each individual cycle represents a single sealevel rise. Sensitivity testing of one-dimensional forward models incorporating a depth threshold of carbonate accumulation indicates that multiple upward-shallowing cycles may originate during any single rise in sealevel. Variation in resultant cycle stacking pattern is sensitive to changes in sealevel amplitude, sedimentation rate, and subsidence rate, with highest stacking ratios (ratio of number of cyclic units to number of eustatic periods) produced by low sealevel amplitudes and high sedimentation and subsidence rates. These relations indicate that direct correlation between multiple-frequency eustatic sealevel variations and meter-scale cycle stacking hierarchies is unwarranted. Thus, prevalent interpretations regarding the stacking record of orbital forcing in ancient carbonate rock sequences should be reevaluated.