Ichnological evidence of rapid recovery after the K-Pg event.

 

Chicxulub impact crater, Yucatan. Credit; D. VAN RAVENSWAAY / SCIENCE PHOTO LIBRARY

Mass extinctions had shaped the global diversity of our planet several times during the geological ages. The fossil record indicates that more than 95% of all species that ever lived are now extinct. The Cretaceous/Palaeogene (K-Pg) mass extinction eradicated almost three-quarters of the plant and animal species on Earth including non-avian dinosaurs, pterosaurs, marine reptiles, and ammonites. The extinction was caused by paleoenvironmental changes associated with the impact of an asteroid. In 1981, Pemex (a Mexican oil company) identified Chicxulub as the site of this massive asteroid impact. The crater is more than 180 km (110 miles) in diameter and 20 km (10 miles) in depth. The impact released an estimated energy equivalent of 100 teratonnes of TNT, induced earthquakes, shelf collapse around the Yucatan platform, and widespread tsunamis that swept the coastal zones of the surrounding oceans. The event also produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. Global forest fires might have raged for months. Photosynthesis stopped and the food chain collapsed. Marine environments lost about half of their species, and almost 90% of Foraminifera species went extinct.

New evidence from the International Ocean Discovery Program (IODP) Expedition 364 showed a surprisingly rapid initial tracemaker community recovery after the K-Pg mass extinction event. The trace fossil assemblage mainly consists of Chondrites, Zoophycos, Planolites, and Thalassinoides, characterizing a multitiered ichnofauna from the Zoophycos ichnofacies. Trace fossil assemblages can be divided according the palaeoenvironmental scheme into a number of ichnofacies named after a characteristic trace fossil. The Zoophycos Ichnofacies is dominated by trace fossils belonging to the ethological class fodinichnia, consisting of both simple and complex burrows.

Sedimentological and ichnological features through the studied cores, from the Chicxulub impact crater, Yucatán Peninsula. From Rodríguez-Tovar et al., 2020.

Previous studies revealed that porous rocks in the center of the Chicxulub crater remained hotter than 300 °C for more than 100,000 years. The high-temperature hydrothermal system was established within the crater but the appearance of burrowing organisms within years of the impact indicates that the hydrothermal system did not adversely affect seafloor life. These impact-generated hydrothermal systems are hypothesized to be potential habitats for early life on Earth and other planets.

The trace fossil assemblages indicate that recovery occurred within several years after the K-Pg transition with scarce, small, Planolites (a walled burrow tube made by a deposit feeder). Followed by a first phase of diversification with Planolites, Chondrites, and Palaeophycus, as well as a shallow indeterminate infauna. This community stabilized, with changes only in relative abundance until ∼640000- 700,000 years into the Paleocene. The appearance of Zoophycos marks the beginning of the highest diversity, abundance, and size of traces, and reveals that the Zoophycos ichnofacies was completely established and maintained to the top of the studied interval ∼1.25 m.y. after the K-Pg event. Comparison between the end-Permian mass extinction and the K-Pg record indicates similar overall patterns of recovery after both events, although the K-Pg recovery was significantly faster.

 

References:

Francisco J. Rodríguez-Tovar et al, Rapid macrobenthic diversification and stabilization after the end-Cretaceous mass extinction event, Geology (2020). DOI: 10.1130/G47589.1

 

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