Remarks on the supposed bolid impacts at the T/J boundary in the Corfino Section (Northern Apennines, Italy)

Abstract

In 1991, American scientists found “shocked” quartz grains, indicating extraterrestrial bolide impacts,near Corfino (Northern Tuscany) in shaly beds at the boundary between the Rhaetian Calcare a Rhaetavicula and the inferred Lower Jurassic (Hettangian) Calcare Massiccio. According to our observations of the same section, the top interval of the Calcare a Rhaetavicula consists of beds of oolitic grainstone, interlayered with thin levels of marls where the shocked quartz grains were found. In the overlying Calcare Massiccio the rock consists mostly of dolomitised and recrystallised mudstone up to about 30 m, where abundant Rhaetian benthic foraminifers occur. The occurrence of shocked quartz in the upper part of the Calcare a Rhaetavicula suggests that one or more impact events took place at this time; however, Triassic fossils occur well above the shocked quartz levels and any impact events therefore occurred within the Rhaetian.