Immediate and Postevent Effects of the K/Pg Boundary Chicxulub Impact on the Northern Gulf of Mexico
Published:December 01, 2012
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Scott Erik, Denne Richard, Kaiser James, Eichkoff David, 2012. "Immediate and Postevent Effects of the K/Pg Boundary Chicxulub Impact on the Northern Gulf of Mexico", New Understanding of the Petroleum Systems of Continental Margins of the World, Norman C. Rosen, Paul Weimer, Sylvia Maria Coutes dos Anjos, Sverre Henrickson, Edmundo Marques, Mike Mayall, Richard Fillon, Tony D’Agostino, Art Saller, Kurt Campion, Tim Huang, Rick Sarg, Fred Schroeder
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The Chicxulub bolide impact on the Yucatan peninsula at the Cretaceous-Paleogene (K/Pg) boundary has been postulated as the trigger that remobilized sediment into mass transport flows on the submerged shelf along eastern North and Central America as well as around the Gulf of Mexico and redistributed sediment out into the deep water Atlantic, Caribbean, and Gulf of Mexico. Well log and biostratigraphic data from Cretaceous well penetrations in the deep-water northern Gulf of Mexico show a distinctive micritic deposit at the K/ Pg boundary that is similar in composition and biostratigraphy to sediments found near the Chicxulub crater, DSDP/ODP cores, and outcrops in Cuba. Investigation of seismic data in the northern Gulf of Mexico shows anomalous sedimentary wedges of high amplitude reflectors situated at the top of the Cretaceous section that are interpreted to be the resulting deposit from the mass transport flows and suspension fallout initiated by the impact.
At the end of the Cretaceous, the northern Gulf of Mexico was undergoing allocthonous salt movement from the Jurassic Louann Salt that was expressed in numerous salt highs defining potential clastic sediment fairways. The sediment redistribution caused by the Chicxulub impact filled in the available accommodation space around the salt highs, as well as depositing on the highs themselves, and altered the seafloor topography across the northern Gulf of Mexico. This resulted in an efficient transportation pathway from shelf to deep water and influenced the sedimentation patterns of the subsequent sediment gravity flows of the Wilcox Formation.
Sediment Reworking into the Deep-Water Gulf Of Mexico
The Chicxulub impact is estimated to have caused a magnitude 11 earthquake tsunamis 100-300 m in height, and spread ejecta material around the globe (Schulte et al., 2010). Three formations in Cuba have been identified as K/Pg sections deposited in the “deep-water” of the proto-Caribbean Sea and then scraped onto the island as it moved northward to its current position. From K/Pg sections in Cuba, Tada et al. (2003) and Goto et al. (2008) describe the Moncada Formation as a thin (~2 m) calcarenite deposited on the paleoslope, while the much thicker Cacarajicara Formation (up to 700 m) and portions of the Peñalver Formation (up to 180 m) were deposited in a basinal setting (Fig. 1). The Cacarajicara and Peñalver formations are comprised of a basal carbonate breccia up to 275 m thick formed by the collapse of the Campeche carbonate platform. The upper portions of the deposits are composed of a calcarenite that grades upward into a calcilutite showing no discernible break in deposition or signs of bioturbation.
In seventeen wells drilled by industry in the deep water (> 300m) northern Gulf of Mexico that penetrated the K/Pg boundary (Fig. 2), a layer was identified immediately below the recognized K/ Pg boundary that contained a unique assemblage of biostratigraphic markers as a result of sediment mixing initiated by the Chicxulub impact (Bralower et al., 1998). Thicknesses of this deposit in the wells range from over 200 m in the western Gulf of Mexico to less than 20 m in the east. Full penetrations of the impact deposit in the Alaminos Canyon 557 #1BP2, Keathly Canyon 596#1, and Keathly Canyon 102#1 wells show thick massive, micritic limestone sitting atop interbedded calcareous shales and limestones (Fig. 3). The thick limestone is identified on well logs by a strong, consistently low gamma-ray response coupled with a high resistivity reading and contains the unique biostratigraphic assemblage related to the Chicxulub impact. The other well penetrations all show the high gamma ray and resistivity readings as they enter the interval containing the diagnostic biostratigraphic assemblage. Underlying the impact deposit in all the wells is an unconformity surface that represents varying amounts of missing time, from the Maastrictian to mid-Campanian in all the penetrations, and locally, into the Jurassic (Fig. 4).
Seismic data from the Keathly Canyon show an anomalous facies of multiple high-amplitude onlapping seismic reflections at the top of the Cretaceous section (Figs. 5–7) that exhibits a wedge up to 800 m of thickness which has a roughly rounded or oval map pattern, implying a fill of a topographic low. The seismic wedges contain multiple seismic reflections indicating layering of the sediments as seen in the Cuban outcrops and from well logs. The thickness and geometry of the seismic wedges indicate that numerous topographic lows existed in the seafloor in the central northern Gulf of Mexico in the late Cretaceous that were related to salt movement and filled in by sediment gravity flow (debris flow or turbidity current) initiated from the Chicxulub impact.
Chicxulub Impact Depositional Model
The sediment deposition across the northern central Gulf of Mexico is predominately carbonate muds of minimally varying thickness due to slow sedimentation rates. Topographic variations in the seafloor are present related to the development of salt diapirs (Fig. 8).
Earthquake waves and tsunamis radiated out from the impact center across the Gulf of Mexico shaking water-laden sediments on the shelf and slope across the entire northern Gulf of Mexico. The earthquakes and tsunamis disturbing and resuspending the nonindurated sediments into the water column as well as triggering sediment gravity flows across the northern Gulf of Mexico (Fig. 8).
Slope failures produced sediment gravity flows and transported sediments, along with the larger ejecta material to the available accommodation space in the deep water Gulf of Mexico. The different sediment supply areas (e.g., local highs, slope and shelf areas) had transport paths of different lengths that resulted in the layering of material in the receiving basin sourced from different sites (Fig. 8).
Ejecta material and resuspended sediments (silt size) settle onto the sea floor draping most locations. Sediment gravity flows continue to transport sediments to the deep water Gulf of Mexico (Fig. 8).
Sediment gravity flows stop as all sediment that could have moved has done so. The finest grained sediments (clay size) settle from the water column and drape most locations (Fig. 8).
Effect of the Impact Deposit on the Gulf of Mexico Sea Floor
The basin-wide redistribution of sediment from local highs, the shelf, the slope and possibly even onshore locations, filled in topographic lows smoothing the sea floor but did not completely cover all the salt highs (Fig. 9). The overlying clastic sediments of the Paleogene/Eocene Wilcox Formation were funneled along the clastic sediment fairways defined by salt highs from the shelf into the deep water. The smooth topography from the filling of available accommodation space on the slope established an efficient transportation pathway for the Wilcox sediment gravity flows. As the sediment gravity flows exited these corridors they formed coalescing distributary complexes.
The Chicxulub impact initiated nearly simultaneous movement of sediment by “ordinary processes” over an immense geographic area, resulting in the most significant single depositional event in the history of the Gulf of Mexico.
Figures & Tables
New Understanding of the Petroleum Systems of Continental Margins of the World
- Alaminos Canyon
- Atlantic Ocean
- Caribbean region
- chemically precipitated rocks
- Chicxulub Crater
- deep-water environment
- geophysical methods
- geophysical profiles
- geophysical surveys
- gravity flows
- Greater Antilles
- Gulf of Mexico
- impact features
- K-T boundary
- lower Paleocene
- mass movements
- North Atlantic
- salt tectonics
- sedimentary rocks
- seismic methods
- seismic profiles
- stratigraphic boundary
- Upper Cretaceous
- well logs
- West Indies
- Wilcox Group
- Yucatan Peninsula
- Penalver Formation
- Cacarajicara Formation
- Moncada Formation
- Keathly Canyon