Parameters of the Cretaceous-Tertiary Boundary Impact Event

Impact Events at the Cretaceous-Tertiary Boundary

“…At the same time, numerous finds in this horizon of shock-metamorphosed grains of quartz, sodic plagioclase and potash feldspar [157,188,194,212] require the presence of continental-crust components in the K-T crater ejecta. Estimates of the amount of crater ejecta scattered on a global scale [93] at the K-T boundary suggest that basaltic material is sharply dominant in their composition, and their calculated mass is consistent with the formation of a large crater, up to 250 km in diameter, in oceanic crust. To explain the observed amount of shock-metamorphosed quartz in the boundary deposits, the oceanic target would have to have contained about 6% of upper crustal material, for instance in the form of clastic sediments, overlying oceanic basalts.…”

“…It appears that at the Cretaceous-Tertiary boundary a huge impact event occurred in the ocean, accompanied by the formation of a relatively small crater (or craters) on continental crust. Estimates [93] suggest that the main crater would have been formed by a cosmic body weighing more than 0.6 • 10 18 , but less than 10 1 g.…”

“…On the whole it can be concluded that the Kara and probably the Donets crater groups were formed by impacting bodies containing chondritic material. The cosmic component of the K-T boundary deposits also has chondritic properties, and an important feature of the cosmic material in the boundary horizon is a deficit in nickel [93].…”

“…High contents of titanium and vanadium in the Cretaceous-Tertiary boundary horizon [93,248], as well as isotope data [267], lead to the conclusion that the crater ejecta was mainly basaltic material, corresponding to oceanic crust. At the same time, numerous finds in this horizon of shock-metamorphosed grains of quartz, sodic plagioclase and potash feldspar [157,188,194,212] require the presence of continental-crust components in the K-T crater ejecta.…”

“…] shows, greater liberation of heat in the impacting body causes greater scattering of its material and of a finely divided terrigenous component of the ejecta into the upper layers of the atmosphere and dispersion of that material to very great distances. The qualitative and quantitative relationships between the mass of ejecta, which characterizes the energy, and the mass of the impacting body for the K-T event impose narrow constraints on the parameters of iron and chondritic impacting bodies, in contrast to comets, thereby making the latter the most probable type of body causing the K-T event [93].…”