A record of the Precambrian-Cambrian transition in SW Montana: A Late Neoproterozoic to Early Cambrian stratigraphic window, Fortunian biostratigraphic assemblage and Treptichnus pedum

Author

R. Reid Trippe, University of Montana, MissoulaFollow

Year of Award

2019

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geosciences

Department or School/College

Department of Geosciences

Committee Chair

Dr. James W. Sears

Commitee Members

Dr. Marc S. Hendrix, Dr. Andrew Ware

Keywords

southwestern Montana Late Neoproterozoic to Early Cambrian stratigraphy, Treptichnus Pedum trace-fossil, Montana stratigraphic record of the Precambrian-Cambrian transition, the Humbolt anticline

Subject Categories

Geology | Paleontology | Sedimentology | Stratigraphy | Tectonics and Structure

Abstract

This study documents a Late Neoproterozoic through Early Cambrian stratigraphic record in the Humbolt anticline of southwestern Montana. The Precambrian-Cambrian transition includes a Fortunian-aged biostratigraphic trace-fossil assemblage with the ichnofossil Treptichnus pedum. The Humbolt anticline represents an inverted paleo-graben that exposes a stratigraphic window interpreted to be a record of rifting along the Cordilleran miogeoclinal margin, linked with the breakup of the Rodinia supercontinent. The graben subsided and captured sediment during late-stage rifting and final-stage dissociation along the rift margin. Its structural axis paralleled the rift margin. Sevier/Laramide orogenic thrusting inverted the graben into the Humbolt anticline. The Late Neoproterozoic to Early Cambrian section was previously interpreted as belonging to the Mesoproterozoic Belt Supergroup and Middle Cambrian strata. The Fortunian-aged biostratigraphic assemblage is distinguished by the appearance of Treptichnus pedum,the ichnospecies that defines the Global Standard Point for the Precambrian-Cambrian boundary. This work correlates the upper part of the Humbolt anticline’s stratigraphy to the Chapel Island Formation in Newfoundland Canada, the Wood Canyon Formation and Zabriskie Quartzite in Death Valley USA, and other Latest Neoproterozoic to Early Cambrian successions along western North America’s Cordilleran margin.

Recommended Citation

Trippe, R. Reid, 2019, A record of the Precambrian-Cambrian transition in SW Montana: A Late Neoproterozoic to Early Cambrian stratigraphic window, Fortunian biostratigraphic assemblage and Treptichnus pedum: Graduate Thesis, University of Montana, Missoula, USA.