Evidence of Climate Change During Carnian Triassic

Sequence stratigraphy after the demise of a high-relief carbonate platform (Carnian of the Dolomites): sea-level and climate disentangled

Authors:

Gattolin et al

Abstract:

Sedimentary facies analysis aided by quantitative 3D georeferenced field data are applied to constrain the sequence stratigraphy of a complex stratigraphic interval in the Late Triassic of the Dolomites. This multidisciplinary approach was the key to disentangle the timing of climatic change vs. sea-level fluctuation and their effects on shallow water carbonate depositional systems. The “Carnian Pluvial Event”, a global episode of climate change worldwide documented at low latitudes, involved increased rainfall and possibly global warming. This climatic event begins before a drop of sea-level and caused the demise of microbial-dominated high-relief carbonate platforms that dominated the Dolomites region, and was followed by a period of coexistence of small microbial carbonate mounds and arenaceous skeletal-oolitic grainstones. A subsequent sea-level fall brought to the definitive disappearance of microbialites and shallow water carbonates switched to ramps dominated by oolitic-bioclastic grainstones. The crisis of early Carnian shallow water carbonate systems of the Dolomites generated a geological surface similar to a drowning unconformity, although no transgression occurred. As the high-relief microbial carbonate systems characterized by steep slopes switched to gently inclined oolitic-skeletal-siliciclastic ramps, basins were rapidly filled. The change of carbonate depositional systems was associated with an increase in siliciclastic input, in turn triggered by the onset of a humid climatic event and only later to a sea-level drop. This evolution of carbonate systems cannot be interpreted in the light of sea-level changes only: climate change, and consequent ecological changes in the main carbonate producing biotas, induced significant modifications in depositional geometries. This case study may serve as a conceptual model for the sedimentary evolution of carbonate systems subject to ecological crisis that do not evolve in platform drowning because, despite a drop in shallow water carbonate production, a combination of low subsidence and/or sea level drop maintains the platform top at shallow depth.