ABSTRACT: Significance of Lignites in Paleocene Middle Wilcox Stratigraphy in East Central Louisiana
GODDARD, DONALD, and JOHN ECHOLS, Basin Research Institute, Louisiana State University, Baton Rouge, LA, and PAUL COMET, Geochemical and Environmental Research Group, College of Geosciences and Maritime Studies, College Station, TX
Lignites are a ubiquitous component of the stratigraphic sequence in the deltaic depositional environment of the Wilcox Group. In the middle Wilcox, between the Big Shale and the upper Minter oil sands, 11 principal lignites, ranging in thickness from a few inches to 5-10 ft, have been observed on E-logs and corroborated by conventional cores and sidewall samples.
These extensively correlative lignites commonly overlie distributary channels and overbank bay fills. The lignites are usually overlain by shales indicating that compactional subsidence or sea level rise returned the area to shallow marine conditions. Assuming a lower delta-plain setting, the upper lignite surfaces commonly represent marine-flooding surfaces or parasequence boundaries. Peat accumulation resulting in lignites appears to represent only minor hiatuses between aggradational sands and interdistributary bay marine deposits.
Productive Minter oil sands (2-12 ft) are closely associated with lignites and may be bounded above and below by them (Bee Brake and North Bee Brake fields). These lignites possibly act as oil migration conduits. Organic petrography and geochemistry indicate that they are good potential source rocks for hydrocarbons. The association of these lignites with possible methane gas production is as yet an uninvestigated possibility in east-central Louisiana.
AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)