When you propose a site to be drilled you have to make assumptions about what you kinds of rocks you want to target; how old they will be, how deep they are buried and thus the resource required to run the drilling Expedition. For Chicxulub we decided to start collecting core 500 m below the seafloor with the idea that this would be within the Eocene, a time known to be the hottest planet Earth has been throughout the entirety of the Cenozoic (the last 66 million years). We would then core through the transition into the Paleocene, which was the 10 million years that followed the impact event, to see how life recovered. Finally, we would drill into whatever the boundary layers would be and onward into the peak ring itself. We picked depths at which we expected to cross key boundaries and made the assumption it would be a complete record.
Without giving too much away, we have already had some amazing surprises. The Eocene section in the borehole was really thick, there were possibly two unconformities (meaning some time is missing from the record), and the boundary layer itself was encountered shallower, and is much thicker, than anticipated.
It is also particularly interesting to think about the layers of rock we have cored. We have cases where we collected meters and meters of sediment, likely representative of the events that happened within the first few hours to days after the impact. In other cases, single cores of 1.5 m represent millions of years of slow deposition and time gaps.
So now we drill into the peak ring itself and we are expecting more surprises.
Sean Gulick – Co-chief Scientist