The 'Ladinian–Carnian Terrigenous Invasion' Revisited: Clues from the Petrography of Sandstones and Shales in Northwestern Bulgaria

Abstract

Increased siliciclastic influx caused temporary cessation of the carbonate sedimentation on a NW Tethyan ramp around the Middle/Late Triassic boundary. This regional 'Ladinian–Carnian terrigenous invasion' has been formerly interpreted as a result of intensive tectonic activity in the sourceland. However, new petrographic data from sandstones and shales outcropping in NW Bulgaria reveal that the major control was climate humidification. The latter is evidenced by the high quartz/feldspar ratio, very low amount of plagioclase, lithic grains and unstable detrital minerals, traces of corrosion in many quartz grains, and authigenic glauconite formation in the sandstones as well as the abundance of phytoclasts and presence of amber in the shales (plus a hygrophytic affinity of the spore-pollen assemblage as determined in a previous research). The significant climate change was most likely associated with the 'Ladinian–Carnian humid interval' which has been recognized in Tethyan and Peri-Tethyan successions across Europe and explained as a consequence of intense volcanism. The termination of massive siliciclastic input was followed by renewed carbonate deposition in the ramp environment indicating a rapid return to arid climatic conditions before the onset of the global 'Carnian Pluvial Event'.