T134 Oceans and Climates through Earth History: From Proxy Reconstructions to Model Assessments (Posters)

Wednesday, 28 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

SILICATE WEATHERING AND MIDDLE DEVONIAN PALEOCLIMATE

Paper number: T134-4
Program: Technical Sessions
Time: 2:00 PM – 2:10 PM

Authors

Abstract

Chemical weathering of Ca- and Mg-bearing silicate minerals and the subsequent trapping of carbon in marine carbonates act as a sink for atmospheric CO2, driving shifts in global climate on geologic time scales. However, the role of silicate weathering in the fluctuating paleoclimate of the Devonian Period (419 to 359 Ma) is poorly understood. Although the Devonian Period has been generally regarded as a greenhouse climate, previous paleotemperature studies suggest that sub-tropical sea surface temperatures (SST) cooled considerably during the late Early to Middle Devonian before warming again in the early Late Devonian.

This study aims to constrain the role of silicate weathering in the warming climate of the late Middle Devonian. Strontium isotopes (87Sr/86Sr) act as a geochemical proxy for the lithology of weathered silicates. Marine conodont apatite samples from Pic de Bissous, France had previously been analyzed for SST via the paleotemperature proxy δ18O (Joachimski et al., 2009). We analyzed these same samples for 87Sr/86Sr, creating complementary δ18O and 87Sr/86Sr curves with no temporal uncertainty between them. We found that 87Sr/86Sr inflects toward more radiogenic values within 1 My of when δ18O shifts to lower (warmer) values in the mid-Givetian (ca. 383 Ma), suggesting a link between silicate weathering and climate warming. We hypothesize that cool ocean bottom water of the Early to Middle Devonian reduced the rate of alteration to ocean crust, reducing carbon sequestration in hydrothermal systems along with weathering of low-87Sr/86Sr oceanic crust (cf. Coogan and Dosso, 2015). A reduced rate of subaerial basalt weathering would produce similar results. Either mechanism results in higher pCO2 and warming, which would increase weathering of high-87Sr/86Sr continental crust.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-353865

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