Repeated subaerial exposure of subtidal carbonate platforms, Triassic, northern Italy: Evidence for high frequency sea level oscillations on a 104 year scale


  • Lawrence A. Hardie,

  • Alfonso Bosellini,

  • Robert K. Goldhammer


Triassic carbonate platforms in northern Italy (Ladinian Latemar, Carnian Durrenstein, Norian Dolomia Principale) consist of hundreds of stacked meter-scale cycles each made of a subtidal unit with a cap rock that carries vadose cements, pisoids, and tepee structures. These diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments. The absence of peritidal deposits rules out progradation as the cause of the exposure; i.e., these are not Ginsburg autocycles. Thus the repeated exposure must be the result of relative sea level oscillations, which, based on the number of cycles and time intervals involved, occurred with an average frequency in the 104 -year range. We postulate a combination of small-scale, high-frequency eustasy and local tectonic movements (e.g., differential subsidence in the Norian and infrequent pulses of uplift in the Ladinian) to explain the cyclicity and its internal variations.