THE PERMIAN-TRIASSIC OF EASTERN COLORADO: REDBEDS, SLIME, SALT, DUNES, AND POSSIBLY AN EXTINCTION?

The Lykins Formation and its equivalents in Colorado, a suite of redbeds and intercalated stromatolitic carbonates, are hypothesized to span the Permian-Triassic Boundary (PTB). To refine understanding of the age and depositional history of these strata, we logged sixteen reference sections through the Lykins and its equivalents, and here present a preliminary chemostratigraphy, detrital zircon geochronology, biostratigraphy and environmental framework for exposures along the Front Range and in southeastern Colorado.

Conodonts, together with other vertebrate, invertebrate, microfossil, and trace fossils, suggest a very shallow to emergent marine origin for the unit’s most substantial carbonates and intercalated gypsum-anhydrite members. Conodonts from the lower Lykins Formation indicate Middle Permian (Guadalupian) deposition for the lower portion of the Lykins. δ¹³C and ⁸⁷Sr/⁸⁶Sr stratigraphy through the unit is internally consistent with deposition of the Lykins across the PTB interval. Youngest concordant detrital zircons do not exclude deposition of the uppermost Lykins Formation during a portion of Early Triassic time. Detrital zircons from the uppermost Lykins and an overlying eolianite unit consist of a complex and highly diverse primary and multi-cycle grain population transported from eastern Laurentia. They include Appalachian, Grenvillian, and Gondwanan terrane signatures, and transport modes that include wind and water. Conodont alteration indices of 1 indicate the unit has a shallow burial history and is amenable to paleomagnetic inquiry. Considered together, these data help better frame the Lykins and its equivalents, providing a springboard for understanding their records of Permian-Triassic events.