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We present a refined global Furongian (late Cambrian) time scale derived through the application of Bayesian age modeling, using an integrative assemblage of conditioning likelihoods (age constraints) including U-Pb zircon maximum depositional ages in the Steptoean positive isotopic carbon excursion (SPICE) reference section in Smithfield Canyon (Utah, USA) and nearby McPherson Canyon (Idaho, USA); Re-Os geochronology from the SPICE-bearing interval of the Andrarum-3 core (Scania, Sweden); and new high-precision chemical abrasion−isotope dilution−thermal ionization mass spectrometry U-Pb zircon tuff ages from Avalonian Wales. We embed these radioisotopic ages within a novel probabilistic treatment of biozones to establish temporal constraints on rock accumulation rates in the Great Basin (USA), the duration of the SPICE event, and Laurentian trilobite biozones correlated to the global Cambrian time scale. Results reveal a beginning of 494.5 (+0.7/−0.6) Ma and an end of 487.3 ± 0.08 Ma for the Furongian Epoch, representing a reduction of the traditional late Cambrian by ∼30% and an extension of the Ordovician by nearly half a million years. Furthermore, the SPICE is confined to a duration of 2.6 (+0.9/−0.8) m.y. Our new approach to integrating faunal succession into Bayesian age modeling can help to constrain rock accumulation rates and possible hiatuses in sections with limited radioisotopic ages. Additionally, it offers a robust calibration tool for further refining the numerical calibration of the geologic time scale, for testing hypotheses about the rates of trilobite evolution and extinction, for evaluating causes of the SPICE, and for constraining paleoclimatic conditions including atmospheric O2 levels. 

The fossil record of the U.S. Pacific Northwest preserves many Middle Miocene floras with potential for revealing long-term climate-vegetation dynamics during the Miocene Climatic Optimum. However, the possibility of strong, eccentricity-paced climate oscillations and concurrent, intense volcanism may obscure the signature of prevailing, long-term Miocene climate change. To test the hypothesis that volcanic disturbance drove Middle Miocene vegetation dynamics, high-resolution, stratigraphic pollen records and other paleobotanical data from nine localities of the Sucker Creek Formation were combined with sedimentological and geochemical evidence of disturbance within an updated chronostratigraphic framework based on new U-Pb zircon ages from tuffs. The new ages establish a refined, minimum temporal extent of the Sucker Creek Formation, ~15.8 to ~14.8 Ma, and greatly revise the local and regional chronostratigraphic correlations of its dispersed outcrop belt. Our paleoecological analysis at one ~15.52 Ma locality reveals two abrupt shifts in pollen spectra coinciding with the deposition of thick ash-flow tuffs, wherein vegetation dominated by Cupressaceae/Taxaceae, probably representing aGlyptostrobus oregonensisswamp, and upland conifers was supplanted by early-successional forests with abundantAlnusandBetula. Another ephemeral shift from Cupressaceae/Taxaceae swamp taxa in favor of upland conifersPinusandTsugacorrelates with a shift from low-Ti shale to high-Ti claystone, suggesting a link between altered surface hydrology and vegetation. In total, three rapid vegetation shifts coincide with ash-flow tuffs and are attributed to volcanic disturbance. Longer-term variability between localities, spanning ~1 Myr of the Miocene Climatic Optimum, is chiefly attributed to eccentricity-paced climate change. Overall, Succor Creek plant associations changed frequently over ≤10⁵years timespans, reminiscent of Quaternary vegetation records. Succor Creek stratigraphic palynology suggests that numerous and extensive collection of stratigraphically controlled samples is necessary to understand broader vegetation trends through time. 

Abstract The Southwestern Laurentia large igneous province (SWLLIP) comprises voluminous, widespread ca 1.1 Ga magmatism in the southwestern United States and northern Mexico. The timing and tempo of SWLLIP magmatism and its relationship to other late Mesoproterozoic igneous provinces have been unclear due to difficulties in dating mafic rocks at high precision. New precise U-Pb zircon dates for comagmatic felsic segregations within mafic rocks reveal distinct magmatic episodes at ca. 1098 Ma (represented by massive sills in Death Valley, California, the Grand Canyon, and central Arizona) and ca. 1083 Ma (represented by the Cardenas Basalts in the Grand Canyon and a sill in the Dead Mountains, California). The ca. 1098 Ma magmatic pulse was short-lived, lasting 0.25−0.24+0.67 m.y., and voluminous and widespread, evidenced by the ≥100 m sills in Death Valley, the Grand Canyon, and central Arizona, consistent with decompression melting of an upwelling mantle plume. The ca. 1083 Ma magmatism may have been generated by a secondary plume pulse or post-plume lithosphere extension. The ca. 1098 Ma pulse of magmatism in southwestern Laurentia occurred ~2 m.y. prior to an anomalous renewal of voluminous melt generation in the Midcontinent Rift of central Laurentia that is recorded by the ca. 1096 Ma Duluth Complex layered mafic intrusions. Rates of lateral plume spread predicted by mantle plume lubrication theory support a model where a plume derived from the deep mantle impinged near southwestern Laurentia, then spread to thinned Midcontinent Rift lithosphere over ~2 m.y. to elevate mantle temperatures and generate melt. This geodynamic hypothesis reconciles the close temporal relationships between voluminous magmatism across Laurentia and provides an explanation for that anomalous renewal of high magmatic flux within the protracted magmatic history of the Midcontinent Rift.