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Palynology and microstratigraphy of Cretaceous-Tertiary boundary sections in southwestern North Dakota

December 1, 2002

Palynology is used to bracket or pinpoint the Cretaceous-Tertiary (K-T) boundary in 17 measured sections near the contact of the Hell Creek Formation and the Ludlow Member of the Fort Union Formation in southwestern North Dakota. Palynostratigraphy is the most reliable method for locating the K-T extinction horizon - which defines the K-T boundary - in nonmarine rocks. The palynological database includes 110 taxa for which relative abundance or presence or absence data were recorded in more than 350 samples based on surveys of more than 700 000 specimens. These data from laterally extensive outcrops in the badlands along the Little Missouri River provide a temporal framework for concurrent studies in the area on megafossil paleobotany, vertebrate paleontology, lithostratigraphy, magnetostratigraphy, and chemostratigraphy. Palynology demonstrates extinction of 30% or more of the Maastrichtian palynoflora, including characteristic Maastrichtian taxa ("K taxa"), at the K-T boundary. Most of the palynomorph taxa discussed probably represent higher-level plant taxa (botanical genera or families). The K-T boundary is shown to be coincident with the Hell Creek-Fort Union formational contact at only two localities; it is as much as 2.7mabove the base of the Fort Union Formation at others. Thus, a distinctive interval of Fort Union strata of Cretaceous age is recognized that is characterized by occurrences of numerous K taxa, usually in low percentage abundance, up to the K-T boundary. This interval documents a regional paleoenvironmental change that is independent of the extinction event and that is important to understanding the K-T transition throughout western North America.

Publication Year 2002
Title Palynology and microstratigraphy of Cretaceous-Tertiary boundary sections in southwestern North Dakota
DOI 10.1130/0-8137-2361-2.95
Authors Douglas J. Nichols, K.R. Johnson
Publication Type Article
Publication Subtype Journal Article
Series Title Geological Society of America Special Papers
Index ID 70221505
Record Source USGS Publications Warehouse