AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
The K/Pg Boundary Chicxulub Impact Deposit in the Deep-Water Gulf of Mexico: Implications for Regional Stratigraphy and the “MCU”
(1) Marathon Oil Company, Houston, TX.
Although numerous academic studies have examined outcrops and Deep Sea Drilling Program (DSDP) / Ocean Drilling Program (ODP) cores to determine the effects of the Cretaceous / Paleogene (K/Pg) boundary Chicxulub Impact located on the Yucatan Peninsula both globally and along the margins of the Gulf of Mexico, the energy industry has not fully recognized the considerable impact this event had on the deep-water Gulf of Mexico, with the exception of the world-class Cantarell field which was partially created by the Chicxulub Impact. Initial penetrations of the K/Pg boundary in the deep-water were drilled by DSDP Legs 10 and 77 in the southeastern Gulf of Mexico in the 1970's. The term Middle Cretaceous Unconformity (MCU) was coined for what was then believed to be an unconformity identified in the cores between the Upper and Lower Cretaceous layers. The “MCU” (or "Middle Cretaceous Sequence Boundary") is a high-amplitude seismic reflector that has been mapped in many studies of the Gulf of Mexico basin. Examination of seismic and released log and biostratigraphic data from 16 Cretaceous penetrations by industry in the deep-water Gulf of Mexico identified a distinctive micritic deposit at the K/Pg boundary ranging from 10 to 200 m (30-600') in thickness that is similar in composition to sediments found within the Chicxulub Crater. This relatively homogenous deposit contains a mixture of Cretaceous (Maastrichtian to Aptian) microfossils and unconformably sits on sediments ranging in age from Campanian to Aptian (or older). These findings suggest that the tsunami-wave and seismic shock generated by the Chicxulub Impact removed most, and at some localities, all of the non-indurated Upper to Lower Cretaceous sediments in the deep-water Gulf of Mexico and nearly instantaneously re-deposited them in basinal lows. This implies that the much thinner boundary deposits found at the basin margins are also a product of the impact, and not the result of a purported low-stand at the boundary as theorized by some authors. Our results are in agreement with recent studies that have indicated that the "MCU" is not an unconformity within the middle Cretaceous, but is an erosional event at the K/Pg boundary produced by the Chicxulub Impact.