CORE-LOG-SEISMIC INTEGRATION IN THE CHICXULUB IMPACT BASIN: PRELIMINARY RESULTS FROM IODP-ICDP EXPEDITION 364

In April and May of 2016, Expedition 364 of the International Ocean Discovery Program cored the peak ring of the Chicxulub impact crater and overlying Paleogene sediments to investigate the formation and post-impact processes of large impact craters. Integration of lithostratigraphic and logging data from the expedition with ~2000 km of seismic reflection data gathered in 1996 and 2005 provides a new opportunity to analyze seismic data of the Chicxulub impact basin.

Core was recovered from Hole M0077A between 505.70 and 1334.73 mbsf, spanning two previously defined seismic units of the crater infill and the underlying impact-derived suevites and basement granites. The lower seismic unit, Unit A, is characterized as a set of strong subparallel reflectors that is thickest in the annular trough and onlaps and thins out over the peak ring. Unit A overlies the impact suevites that define the impact sequence, and is conformably overlain by seismic Unit B. A full waveform inversion of seismic data near the borehole indicates higher velocities within Unit A than the units above and below it, and show Unit A to have a similar thickness and range of depths as lithostratigraphic sub-units 1E, 1F, and 1G (~580 to ~617 mbsf). This potential correlation between the seismic and lithostratigraphic units is supported by downhole sonic log, vertical seismic profile, and discrete velocity measurements on the core. The downhole sonic log obtained seismic velocities ~600 m/s faster in these sub-units than the overlying lithostratigraphic units. Reflection data in seismic lines surrounding the borehole suggest that the lowest reflector of Unit A at the peak ring expands into a package of four or more reflectors within the annular trough. This reflector appears to correspond to stratigraphic units 1F and 1G (the lowest ~10 m of Unit A); biostratigraphic data indicate that the units are Paleocene in age. These units increase in thickness by an order of magnitude from the peak ring to the annular trough, suggesting that these Paleocene deposits could be ~100 meters within the annular trough. If this hypothesis is correct, far more information on the recovery of life within the basin could lie within the sediments infilling the annular trough.