214-6 Estimating late Neoproterozoic-Cambrian temperature conditions for the western Laurentian margin with chemical weathering proxies

Session: The Neoproterozoic Earth and Life Co-evolution, Part II

Presenting Author:

Jaden Olah

Authors:

Olah, Jaden Karl¹, Nelson, Lyle Lee², Webb, Lucy³, Rooney, Alan⁴, Eyster, Athena⁵, Brennan, Daniel Thomas⁶, Mills, Benjamin⁷, Zheng, Dongyu⁸, Sperling, Erik A.⁹

(1) Stanford Doerr School of Sustainability, Port Townsend, WA, USA, (2) MIT, Cambridge, MA, USA, (3) Stanford University, Stanford, CA, USA, (4) Yale University, New Haven, CT, USA, (5) Tufts University, Medford, MA, USA, (6) Montana Bureau of Mines and Geology, Butte, MT, USA, (7) University of Leeds, Leeds, United Kingdom, (8) Chengdu University of Technology, Chengdu, China, (9) Stanford University, Stanford, CA, USA,

Abstract:

     The late Neoproterozoic and early Cambrian saw major swings in global climate broadly coincident with the emergence and diversification of animal life. Recent work in marine ecophysiology has established that the oxygen requirements for sustained metabolic activity are closely related to temperature. Therefore, examining marine oxygen and temperature dynamics in conjunction is critical to obtaining a complete understanding of changing marine environmental habitability. 

    Here, we investigated the temperature dynamics of the late Neoproterozoic and early Cambrian using the Chemical Index of Alteration (CIA) of fine-grained siliciclastic rocks as a paleoclimate proxy. CIA values are calculated by comparing the ratio of immobile Al cations to more mobile cations of Ca, K, Na, yielding an estimate for the degree of chemical weathering, which is a function of temperature along the sediment transport path (albeit with provenance, sorting, and diagenesis as confounding variables). 

    CIA values were calculated from geochemical data obtained from the Sedimentary Geochemistry and Paleoenvironments Project (SGP), plus new data from sites from California to Yukon, for ~1400 fine-grained siliciclastic samples deposited along the western Laurentian margin. Paleogeographic reconstructions place western Laurentia at relatively constant, equatorial paleolatitudes through this time interval, so local temperature fluctuation likely reflects global climate change instead of relative plate motion. Preliminary results reveal the lowest CIA values at ~800 and ~675 Ma with the highest observed values by ~750 and ~650 Ma.  These CIA values broadly track a decrease in global temperature consistent with known glacial intervals through the Cryogenian but reflect cooler Ediacaran and Cambrian temperatures than some other geochemical proxies. Future analyses will use multivariate statistical analyses and machine learning to incorporate grain size, provenance, and estimated paleolatitude as predictor variables, resulting in partial dependence plots tracking CIA through this time interval. Ultimately this will help constrain temperature and climate conditions during critical intervals of early animal evolution. 

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

doi: 10.1130/abs/2025AM-10843

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