Timing and causes of forest fire at the K-Pg boundary

Area of Science:

• Geology
• Paleontology
• Impact Cratering Studies

Background:

• The Cretaceous-Paleogene (K-Pg) boundary marks a mass extinction event.
• The Chicxulub impact is the leading hypothesis for the K-Pg extinction.
• Understanding the immediate environmental consequences of the impact is crucial.

Purpose of the Study:

• To investigate K-Pg age deposits in Baja California, Mexico.
• To interpret these deposits as evidence of the Chicxulub impact and associated mega-tsunami.
• To constrain the timing and extent of impact-induced fires.

Main Methods:

• Analysis of terrestrial and shallow-marine sedimentary deposits.
• Dating of andesitic tuff using SHRIMP U-Pb.
• Identification of shocked quartz, iridium anomaly, and palynological spikes (fungal and fern spores).

Main Results:

• Discovery of K-Pg deposits with corals, gastropods, bivalves, shocked quartz, and charred tree trunks.
• SHRIMP U-Pb dating of tuff yielded an age of 66.12 ± 0.65 Ma.
• Overlying mudstones exhibit an iridium anomaly and spore spikes.
• Charred trees indicate temperatures >1000°C, occurring tens of minutes before tsunami arrival.

Conclusions:

• The heterogeneous deposits are interpreted as a direct result of the Chicxulub impact and a seismically-induced mega-tsunami.
• Tsunami backwash rapidly transported terrestrial flora offshore, remobilizing marine fauna and sediment.
• The findings constrain the timing of fires and the minimum distance from the impact site for fire ignition.