Abstract The Lykins Formation and its equivalents in Colorado are a stratigraphically poorly constrained suite of redbeds and intercalated stromatolitic carbonates, which is hypothesized to span the Permian-Triassic boundary. Herein we present a preliminary detrital zircon geochronology, new fossil occurrences, and δ 13 C chemostratigraphy for exposures along the Front Range and in southeastern Colorado, to refine understanding of the unit’s age and depositional history. Detrital zircons from the uppermost Lykins Formation and an overlying eolianite consist of a complex and highly diverse primary and multi-cycle grain population transported from Laurentian and Gondwanan terranes, potentially both by wind and water. Youngest concordant zircons do not rule out deposition of the uppermost Lykins Formation during a portion of Early Triassic time. Conodonts from the lower Lykins Formation require Middle Permian (Guadalupian) deposition. Conodont alteration indices of 1 indicate the unit has a shallow burial history and is amenable to paleomagnetic inquiry. 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 hint at a marine origin for the unit’s intercalated gypsum-anhydrite members. Chemostratigraphy corroborates field evidence of emergence and karst development capping certain units, like the Forelle Limestone Member of the Lykins Formation, where potential sequence boundaries appear to be punctuated by a short-lived meteoric signature. Results presented here are a progress report of ongoing work in these successions. This field trip consists of a brief tour through exposures of the Lykins Formation, in which we will examine well-known localities as well as view new ones for which we seek insights.

Abstract A middle Pennsylvanian (Desmoinesian) conodont fauna was used to identify the interval represented by the Lower Kittanning cyclothem across the North American continent. The conodonts show both a succession through the cyclothem and a geographic variation that is related to the water mass and depositional environment. The faunas can be divided into normal-marine, high- and (or) variable-salinity, and high-productivity assemblages. Normal-marine faunas are dominated by Idiognathodus , which can be further divided into low-diversity and high-diversity faunas. The low-diversity Idiognathodus faunas characterize the marine deposits of the nearshore, marginal environments of the Appalachian Basin, and also the bulk of the black and gray shale and carbonate depositional environments of Midcontinent cyclothems. The high-diversity Idiognathodus faunas characterize fossiliferous limy shale and shaly limestone depositional environments typical of the shale–limestone transition in Midcontinent cyclothems and the richly fossiliferous limestone deposition in carbonate sequences in much of the western U.S., within the dolomite beds associated with sandstone deposition of the Tensleep Sandstone, and in fossiliferous limestones between sandstones and carbonate mudstones of the Paradox Basin. High-salinity and (or) variable-salinity faunas are dominated by Neognathodus and (or) Adetognathus , and characterize carbonate deposition in the Bird Spring–Ely platform, southwestern U.S., and shallow-water, typically algal facies within the Midcontinent cyclothems. High-productivity faunas are dominated by Gondolella , are extremely rare, and characterize horizons of surface substrate accumulation within black-shale and mud depositional environments. Maximum flooding within the cycle, as indicated by the highest diversity of normal-marine macrobiota and conodont fauna, does not occur in black shales but at the shale–limestone transition. Sixteen species of conodonts in eight genera are recognized in the cyclothem. The following four species are new: Idiognathodus crassadens, I. ignisitus, Neognathodus intrala , and Hindeodus calcarus. Two of these new species, N. intrala and I. crassadens , together with I. robustus , define an assemblage zone that allows correlation of the marine portion of the Lower Kittanning cyclothem across North America.