Novel age constraints for the onset of the Steptoean Positive Isotopic Carbon Excursion (SPICE) and the late Cambrian time scale using high-precision U-Pb detrital zircon ages

Abstract

The Steptoean Positive Isotopic Carbon Excursion (SPICE) is a prominent +4–5‰ shift in the Cambrian δ13C record used for global chronostratigraphic correlation. The onset of this excursion is traditionally placed at the base of the Pterocephaliid trilobite biomere (base of the Furongian Series). Recent studies have documented local controls on the expression of the SPICE and emphasize the need for chronostratigraphic standards for these complex biogeochemical signals. We build upon prior work in western Laurentia by integrating δ13C and biostratigraphy with high-precision isotope dilution U-Pb detrital zircon maximum depositional ages that are coincident with the onset, peak, and falling limb of the SPICE. Our study provides the first useful numerical age constraint for the onset of the SPICE and the Laurentian trilobite biozones and requires revision of the late Cambrian geologic time scale boundaries by several million years.

Cambrian trilobites from the Nounan Dolomite and lower St. Charles Formation (upper Marjuman to lower Sunwaptan; Miaolingian to Furongian Series), Smithfield Canyon, northern Utah

“…The trilobites used for the original biostratigraphy in Smithfield Canyon were identified by Allison Palmer in Saltzman et al (2004), but unfortunately they were never illustrated to allow re-evaluation of the identifications. The recent high-resolution δ 13 C stratigraphic study by Cothren et al (2022) re-documented the SPICE at this section and calibrated it using high-precision chemical abrasion-isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) of detrital zircons, yielding maximum depositional ages (MDAs) of the excursion and additional trilobite collections with preliminary results.…”

“…The Steptoean Positive Isotope Carbon Excursion (SPICE) is an event broadly used for correlation of the Furongian Series worldwide (Saltzman et al, 2004;Geyer, 2019;Peng et al, 2020). The strata containing the SPICE record in northern Utah provides a continuous high-resolution δ 13 C stratigraphy for the upper Miaolingian to Furongian series along with a detailed trilobite biostratigraphy and U-Pb calibrated maximum depositional ages of <494 Ma (Cothren et al, 2022). This combination of features makes this SPICE record in northern Utah probably one of the most important SPICE records in Laurentia and worldwide and allows for testing ideas about correlation, biologic evolution, and the Cambrian timescale.…”

U-Pb zircon dates from North American and British Avalonia bracket the Lower–Middle Cambrian boundary interval, with evaluation of the Miaolingian Series as a global unit

“…U-Pb zircon dates: 483 Ma (Cape Breton Island, Landing et al 1997); 486.8 Ma (North Wales, Landing et al . 2000); 488.7 Ma (North Wales, Davidek et al 1998); 494.36 Ma (Arizona, U. S., Cothren et al 2022, revises Peng et al 2012, of 497 Ma estimate); 503 (Germany, Landing et al 2014); 507.91, 507.67, 506.25 Ma (this report); 508.25 ± 2.75 Ma (New Brunswick, Landing et al 1998, recalculated by Schmitz, 2020); 507.91, 514.45 Ma (England, Harvey et al 2011); 517.2 Ma (England, Williams et al 2013); 526.43 (South China, Yang et al . In Press); 528 Ma (New Brunswick, Isachsen et al 1994, recalculated by Schmitz, 2020); 538 (Namibia, Linnemann et al 2019, reevaluated by Landing et al 2021).…”

“…It has a longer duration than even the entire Upper Cambrian (i.e. Cothren et al 2022). Alternatively, this long duration could hint at potential problems in the correlation and dating of the base of the zone in Avalonian Britain.…”

“…Recently, novel constraints on the timing of the base of the Miaolingian and Furongian epochs have come from detrital zircon studies in western Laurentia (Karlstrom et al 2020;Cothren et al 2022). In this area, precise and accurate chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-IDTIMS) provides U-Pb zircon maximum depositional ages in mixed siliciclastic-carbonate strata of the Tonto Group (Grand Canyon) and Nounan and St. Charles formations (northern Utah) with a west Laurentian trilobite succession (Palmer, 1965;Sundberg et al 2016;Lin et al 2019).…”