Third‐order depositional sequences controlled by synsedimentary extensional tectonics: evidence from Upper Triassic carbonates of the Carnian Prealps (NE Italy)

The Upper Triassic platform‐margin deposits of the Carnian Prealps fail to show the succession of the two global sea‐level lowerings predicted for the Norian and Rhaetian by the Haq global sea‐level curve. In both cases a relative sea‐level rise occurs, a discrepancy that can be explained by an increase in tectonically controlled subsidence, a consequence of the plate‐scale rifting in the NW Tethys Gulf preceding oceanic spreading in the Jurassic. Pulses of tectonic subsidence followed by relative quiescence are capable of generating depositional sequences similar in gross geometry and duration to the third‐order eustatic cycles of Haq et al. The Late Triassic part of the Exxon global sea‐level curve, partly derived from correlatable strata within the same palaeogeographical domain, is likely to reflect pulses of tectonically induced subsidence rather than eustatic sea‐level changes.