Triassic sea level change and the Ladinian–Carnian stage boundary

Abstract

Time–stratigraphie correlations are difficult in many Middle and Upper Triassic sedimentary sections, either because the sections do not contain diagnostic fossils or because of ambiguities in biostratigraphic resolution. Recently, it has been suggested that some Triassic stage boundaries are associated with eustatic changes in sea level^1,2. Here evidence is presented to support that view. Three widely separated examples indicate that the local sea level falls were due to a worldwide change in sea level. At any locality, the response to the global fall in sea level was controlled by the interaction between initial water depth, sedimentation rate and local subsidence rate. In the examples presented here, areas characterized by late Ladinian shallow-water sedimentation show either an erosional unconformity or a seaward shift of facies belts at the Ladinian–Carnian boundary. Late Ladinian slope or basinal settings exhibit shallowing-upward trends, an increase in sedimentation rates, or subtle lithological changes across the boundary. These types of lithostratigraphic relationships can be used to improve correlations in areas where Middle and Upper Triassic sedimentary sections are difficult to date.