On the fate of carbonates and anhydrite in impact processes – evidence from the Chicxulub event

Abstract

In context of the “K/T” Chicxulub cratering event, the amounts of impact-released CO₂ and SO_x as well as the consequences of this gaseous input into the atmosphere are discussed. It has been assumed that degassing of the sediments is an abrupt and violent effect, only related to the amplitude of the post-shock temperature after pressure decay. Here we provide evidence for a different, slow and probably equally important process of devolatilization: degassing and dissociation of sedimentary clasts in impact breccias. The sulfate and carbonate clasts in suevites, melt breccias, and melt rocks from the Chicxulub drill cores Y-6, C-1, and YAX-1, underwent various thermal effects, ranging from solid state re-crystallization over reaction with silicate melt to form pyroxene (diopside), melting (and re-crystallization) to total decomposition with dissolution of the lime in the melt matrix. These features reflect high, yet different formation temperatures of the breccias, and to a smaller degree, the fragment size.

Keywords:

• Chicxulub impact event
• carbonate
• anhydrite
• degassing
• impact metamorphism
• impact melt rocks
• impact breccias
• suevites