25-6 Constraining the Tempo and Dynamics of Cambrian Earth Systems: Unlocking Sedimentary Successions with Tandem Detrital Zircon Geochronology and Bayesian Age Modeling

Session: Refining the Cambrian—Biotas, Multiproxy Correlations, Workable Global Divisions, and Paleogeography: Discussions in Honor of Fred Sundberg

Presenting Author:

Mark Schmitz

Authors:

Schmitz, Mark D.¹, Farrell, Thomas Patrick², Cothren, Hannah R.³, Muhlbauer, Jason⁴, Sundberg, Fred⁵, Dehler, Carol M.⁶, Hagadorn, James⁷, Karlstrom, Karl E.⁸, Crossey, Laura J.⁹, Landing, Ed¹⁰, Westrop, Stephen R.¹¹, Geyer, Gerd¹²

Abstract:

Rocks of the Cambrian Period (539-485 Ma) record dramatic changes in Earth systems including perturbations to the carbon cycle, changes and atmosphere and ocean chemistry, and the Cambrian “explosion” of animal life, all within a series of transgressions of sea level onto continental margins across the Great Unconformity. Although 20^th century U-Pb zircon geochronology and subsequent carbon isotope stratigraphy revolutionized our ability to correlate and calibrate these strata, remarkably few opportunities for further refinement of the Cambrian time scale have arisen in the intervening decades. Southwest Laurentia holds key paleontological and biogeochemical records of Cambrian environments in transgressive fluvio-marine systems exposed from southern Arizona and New Mexico to northern Utah, yet due to a lack of dateable volcanic horizons these records have not played a significant role in calibrating the timing and tempo of Cambrian Earth systems.  In this presentation we review how an interdisciplinary group of scientists have unlocked the potential of these sections using tandem in situ and isotope dilution U-Pb geochronology of detrital zircons and novel Bayesian age models, while testing their global chronostratigraphic significance via renewed efforts in U-Pb zircon ash bed geochronology in the classic Avalonian sequences of Atlantic Canada. These geochronologic and chronostratigraphic insights from Laurentia and Avalonia necessitate reallocations of time within the global Cambrian Period that have implications for the age of the Precambrian-Cambrian boundary, the tempo of trilobite evolutionary rates and extinctions, the amount of organic carbon burial and release during carbon isotope excursions, and the drivers of the Sauk marine transgressions.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8463

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.