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as Paul Lawless and Ryan Weber
present
Upper Cretaceous Erosional Features and the K-Pg Boundary in the Northern GOM Subsurface of Louisiana and Mississippi
Abstract
The HELIS #1 Poitevent, a Tuscaloosa Marine Shale pilot hole in St. Tammany Parish, LA (T7S-R12E-34), drilled 420 feet of chalk section. The chalk section in the area is as much as 1,000 feet thinner than the section 20 miles to the west in Tangipahoa Parish and 40 miles to the north in Washington Parish, or in Pearl River, Stone, and northwest Harrison counties, Mississippi. Foraminiferal and nannofossil analysis of the chalk section cuttings show that the upper 320 feet of the chalk section to be the lowermost Paleogene Danian age. This Danian chalk is likely a downdip expression of the Clayton Formation seen further updip in Mississippi, north Louisiana, and Alabama. Only the lowest 100 feet of the chalk seen in the #1 Poitevent well was actually Cretaceous in age and thought to be equivalent to the Ector Chalk Member of the Austin Group.
The Cretaceous-Paleogene (K-Pg) section in #1 Poitevent well in St. Tammany Parish appears to be similar to that described by Kinsland and Sanford, et al., in a LaSalle Parish core taken in the Justiss #2 LA Central IPNH well, Olla Field, 2-T9N-R2E. Kinsland has interpreted the section seen in the Justiss core to be deposits from the Chicxulub meteor impact in Yucatan. The #1 Poitevent well sits more distally, but still on the stable Upper Cretaceous Shelf. The missing UK Chalk section creating the Pearl Basin Embayment, is shelf edge parallel, is somewhat rectangular, and easily could have broken away from the UK Shelf due to seismicity from the Chicxulub meteor impact. In addition, the Danian chalk samples appear to have been deposited relatively rapidly geologically and appear as a “jumbled mess.”
The second area of thinning lies perpendicular to the Upper Cretaceous Shelf, in the Mississippi Delta counties (Warren, Hinds, Claiborne, Jefferson, Adams, Franklin, Wilkinson, and Amite counties) of the Mississippi Embayment, which crosses into Louisiana in parts of Concordia, Avoyelles, St. Landry, West Feliciana, and East Feliciana parishes. In a regional west-to-east cross-section up-thrown to the UK Shelf Margin, a complete Upper Cretaceous section appears present in Vernon and Rapides parishes. The Upper Cretaceous section thins as much as 1,200 feet in northern Point Coupee and West Feliciana parishes, with an intact Paleogene Danian Clayton Formation sitting above the eroded chalk section, similar to that seen in the Pearl Basin Embayment and on the LaSalle Arch in the Justiss core. On the eastern end of the cross-section in Washington Parish much, but not all, of the Upper Cretaceous section is again observed. Correlations between the north-central Louisiana Upper Cretaceous section to that in Mississippi and Alabama is somewhat difficult because of the Mississippi Delta Incision combined with large thinning and removal of section over the Monroe/LaSalle/Jackson Dome uplifts to the north.
Biographies
Paul Lawless is a petroleum geologist with 34 years of industry experience with several New Orleans-based companies, and he has worked for Helis Oil & Gas over the past 19 years. He holds Bachelor of Science and a Master of Science degrees in Geology from Louisiana State University. He has worked conventional exploration and production in South Louisiana and Southeast Texas, the GOM Shelf and Deep Water, and various resource plays in the Rocky Mountain, Appalachian, East Texas/North Louisiana, South-Central Louisiana/Mississippi, and West Texas basins.
Ryan Weber is currently managing U.S. Business Development for Petrostrat. Prior to merging with PetroStrat, Ryan was president of Paleo-Data, a biostratigraphic consulting firm serving the oil and gas sector for over 50 years. Ryan previously worked for BP as a Gulf of Mexico biostratigrapher. Ryan holds a Bachelor of Science degree and Education certificate from Minnesota State - Mankato, and a Master of Science degree from the University of Nebraska - Lincoln. Ryan also served as Earth Science Section Chair for the Nebraska Academy of Sciences. Ryan’s career has applied biostratigraphy from onshore to deepwater Gulf of Mexico, the interior USA, Egypt Nile Delta, Northwest Australian shelf, offshore Mozambique, Colombia, Alaska, and the Spanish Pyrenees. Ryan’s passions include Miocene and Wilcox stratigraphy, Mesozoic paleooceanography, the Minnesota Twins, and nostalgic comedies.