SUEVITE EMPLACEMENT WITHIN THE CHICXULUB IMPACT STRUCTURE: NEW INSIGHTS FROM THE 2016 IODP-ICDP EXPEDITION 364 DRILLING

The 2016 IODP-ICDP Expedition 364 revealed important new insights in the nature and emplacement of proximal impactites within the Chicxulub impact structure (Yucatán Peninsula, Mexico). In contrast to previous drillings from the southern part of this crater (e.g., Yucatán-6 and Yaxcopoil-1), the Expedition 364 M0077A drill core from the northern peak ring region recovered the first continuous impact melt rock and suevite succession on top of crystalline basement. We studied in detail the petrography, sedimentology, and whole-rock geochemistry of the ∼100-m-thick crater suevite sequence from this drill core to provide a new classification of this rock sequence, and to reconstruct the complex crater infill history of the first moments after the Chicxulub impact.

The M0077A suevite sequence is subdivided into three units that are distinct in their petrography, geochemistry, and sedi­mentology, from base to top: the ∼5.6-m-thick non-graded suevite unit, the ∼89-m-thick graded suevite unit, and the ∼3.5-m-thick bedded suevite unit. All suevite units have isolated Cretaceous planktic foramin­ifera preserved within their clastic matrix, suggesting that marine processes were respon­sible for the deposition of the entire sequence.

We interpret that the first ocean water that reached the northern peak ring (estimated to be <30 minutes after impact) entered through a N-NE gap in the Chicxulub outer rim. This ocean resurge was relatively poor in rock debris and caused intense quench fragmentation when it interacted with the underlying hot impact melt rock, resulting in the formation of the hyaloclastite-like, non-graded suevite unit. In the following hours, the crater was continually flooded by an ocean resurge rich in rock debris, which extinguished phreatomagmatic processes and deposited the ∼89-m-thick graded suevite unit. After the energy of this resurge slowly dissipated, oscil­lating seiche waves took over the sedimentary regime and formed the bedded suevite unit. The upper 20 cm of this unit is cross-bedded and rich in terrestrial biomarkers and charcoal, most probably transported by a reflected turbid tsunami from the nearest landmass in central Mexico. Based on modelling, these reflected tsunami waves have likely re-entered the impact basin within 24 hours after impact, providing a vital upper time constraint for the Chicxulub suevite deposition.