TY - JOUR

T1 - Strontium isotope ratios from the Swabo-Franconian Basin (Germany) and a new compilation of marine 87Sr/86Sr signatures for the Upper Sinemurian to Toarcian: global uniformity and driving forces for marine 87Sr/86Sr

AU - Frederiksen, Jesper Allan

AU - Ullmann, Clemens Vinzenz

AU - Frei, Robert

AU - Korte, Christoph

PY - 2022

Y1 - 2022

N2 - 87Sr/86Sr ratios have frequently been used for correlating marine sedimentary units and its fossils, especially where high fidelity reference curves exist. The latter are usually constructed from macrofossil calcite samples, which have been screened for post-depositional alteration. Here, belemnite rostra from Lower Jurassic (Upper Sinemurian–Upper Toarcian) siliciclastic and carbonate sediments of the Swabo-Franconian Basin, deposited at mid-latitudes in the Laurasian Seaway, were targeted to confirm the trends and absolute values of the marine 87Sr/86Sr reference curve throughout this interval.87Sr/86Sr ratios are derived from 21 belemnite rostra from a wider set of fossil specimens for which preservation was controlled using Scanning Electron Microscopy (SEM) and element/Ca ratios. Taken together with published data, a compilation of >500 87Sr/86Sr data points is established that helps verifying the global significance of the reported trends and allows for the best-constrained reconstruction of marine 87Sr/86Sr across the late Sinemurian-Toarcian interval yet. The obtained results are in excellent agreement with earlier measurements from basins in Portugal, Spain, UK, Germany, and Bulgaria and Canada. 87Sr/86Sr ratios follow the well-known decreasing trend, from 0.70747 in the latest Sinemurian to lowest ratios of 0.70708 around the Pliensbachian–Toarcian boundary. Also the subsequent increase throughout the early Toarcian reaching values of >0.7072 in the early Late Toarcian is found to match previously established datasets.The new results further corroborate a link between marine 87Sr/86Sr ratios and rifting related to the Central Atlantic Magmatic Province throughout the Early Jurassic and increased radiogenic influx, possibly linked to Karoo-Ferrar volcanism and associated climate change in the Early Toarcian which would have likely caused a weathering pulse. The very good agreement in trends and absolute values suggests that macrofossils tapped into an isotopically uniform Sr pool across the Laurasian Seaway even during phases of severe basinal restriction.

AB - 87Sr/86Sr ratios have frequently been used for correlating marine sedimentary units and its fossils, especially where high fidelity reference curves exist. The latter are usually constructed from macrofossil calcite samples, which have been screened for post-depositional alteration. Here, belemnite rostra from Lower Jurassic (Upper Sinemurian–Upper Toarcian) siliciclastic and carbonate sediments of the Swabo-Franconian Basin, deposited at mid-latitudes in the Laurasian Seaway, were targeted to confirm the trends and absolute values of the marine 87Sr/86Sr reference curve throughout this interval.87Sr/86Sr ratios are derived from 21 belemnite rostra from a wider set of fossil specimens for which preservation was controlled using Scanning Electron Microscopy (SEM) and element/Ca ratios. Taken together with published data, a compilation of >500 87Sr/86Sr data points is established that helps verifying the global significance of the reported trends and allows for the best-constrained reconstruction of marine 87Sr/86Sr across the late Sinemurian-Toarcian interval yet. The obtained results are in excellent agreement with earlier measurements from basins in Portugal, Spain, UK, Germany, and Bulgaria and Canada. 87Sr/86Sr ratios follow the well-known decreasing trend, from 0.70747 in the latest Sinemurian to lowest ratios of 0.70708 around the Pliensbachian–Toarcian boundary. Also the subsequent increase throughout the early Toarcian reaching values of >0.7072 in the early Late Toarcian is found to match previously established datasets.The new results further corroborate a link between marine 87Sr/86Sr ratios and rifting related to the Central Atlantic Magmatic Province throughout the Early Jurassic and increased radiogenic influx, possibly linked to Karoo-Ferrar volcanism and associated climate change in the Early Toarcian which would have likely caused a weathering pulse. The very good agreement in trends and absolute values suggests that macrofossils tapped into an isotopically uniform Sr pool across the Laurasian Seaway even during phases of severe basinal restriction.

KW - Faculty of Science

KW - Strontium isotope stratigraphy

KW - Southern Germany

KW - Strontium isotope stratigraphy

KW - Swabo-Franconian Basin

KW - Early Jurassic

U2 - 10.1127/nos/2021/0654

DO - 10.1127/nos/2021/0654

M3 - Journal article

VL - 55

SP - 311

EP - 331

JO - Newsletters on Stratigraphy

JF - Newsletters on Stratigraphy

SN - 0078-0421

IS - 3

ER -