TY - JOUR

T1 - Integrated stratigraphy (radiolarians, calcareous nannofossils, carbon and strontium isotopes) of the Sinemurian–Pliensbachian transition at Mt. Rettenstein, Northern Calcareous Alps, Austria

AU - Cifer, Tim

AU - Goričan, Špela

AU - Auer, Matthias

AU - Demény, Attila

AU - Fraguas, Ángela

AU - Gawlick, Hans-Jürgen

AU - Riechelmann, Sylvia

PY - 2022/4/14

Y1 - 2022/4/14

N2 - A 95 m thick succession of grey siliceous limestone and marl on Mount Rettenstein in the Northern Calcareous Alps allowed us to study well-preserved and diverse radiolarian assemblages across the Sinemurian–Pliensbachian boundary. The distribution of 31 most characteristic radiolarian species is presented. Ammonites of the Jamesoni Subzone, the topmost subzone of the Jamesoni Zone, have been previously found in the upper part of the section. The radiolarian data are complemented with calcareous nannofossil biostratigraphy, and carbon and strontium isotope analyses of bulk carbonate samples. A negative stable carbon isotope excursion (CIE) occurs in the middle part of the section and is correlated to the supraregional Sinemurian – Pliensbachian Boundary Event.Radiolarian assemblages below the negative CIE belong to the Canutus rockfishensis – Wrangellium thurstonense and Jacus? sandspitensis radiolarian zones. Katroma clara and several other species belonging to the subsequent Canutus tipperi – Katroma clara Radiolarian Zone first occur at the beginning of the negative CIE. The first occurrence of the nannofossil Similiscutum cruciulus, which defines the base of the NJ4 Calcareous Nannofossil Zone, was recognized near the top of the negative CIE, 10 m above the inferred stage boundary. The strontium isotope ratio is due to diagenetic alteration of bulk micrite systematically shifted to higher values, but clearly decreases across the stage boundary. This decrease is compatible with the trend of the standard 87Sr/86Sr curve established in skeletal calcite.This is the first time radiolarian zones across the Sinemurian–Pliensbachian boundary in Europe can be tied to calcareous nannofossil zones and chemostratigraphy and also calibrated to chronostratigraphy. These results contribute to the stability of Lower Jurassic radiolarian zones and will allow the recognition of the Sinemurian–Pliensbachian boundary in deep-marine successions where ammonites are absent.

AB - A 95 m thick succession of grey siliceous limestone and marl on Mount Rettenstein in the Northern Calcareous Alps allowed us to study well-preserved and diverse radiolarian assemblages across the Sinemurian–Pliensbachian boundary. The distribution of 31 most characteristic radiolarian species is presented. Ammonites of the Jamesoni Subzone, the topmost subzone of the Jamesoni Zone, have been previously found in the upper part of the section. The radiolarian data are complemented with calcareous nannofossil biostratigraphy, and carbon and strontium isotope analyses of bulk carbonate samples. A negative stable carbon isotope excursion (CIE) occurs in the middle part of the section and is correlated to the supraregional Sinemurian – Pliensbachian Boundary Event.Radiolarian assemblages below the negative CIE belong to the Canutus rockfishensis – Wrangellium thurstonense and Jacus? sandspitensis radiolarian zones. Katroma clara and several other species belonging to the subsequent Canutus tipperi – Katroma clara Radiolarian Zone first occur at the beginning of the negative CIE. The first occurrence of the nannofossil Similiscutum cruciulus, which defines the base of the NJ4 Calcareous Nannofossil Zone, was recognized near the top of the negative CIE, 10 m above the inferred stage boundary. The strontium isotope ratio is due to diagenetic alteration of bulk micrite systematically shifted to higher values, but clearly decreases across the stage boundary. This decrease is compatible with the trend of the standard 87Sr/86Sr curve established in skeletal calcite.This is the first time radiolarian zones across the Sinemurian–Pliensbachian boundary in Europe can be tied to calcareous nannofossil zones and chemostratigraphy and also calibrated to chronostratigraphy. These results contribute to the stability of Lower Jurassic radiolarian zones and will allow the recognition of the Sinemurian–Pliensbachian boundary in deep-marine successions where ammonites are absent.

KW - Early Jurassic

KW - Radiolaria

KW - Calcareous nannofossils

KW - Stable carbon isotopes

KW - Strontium isotopes

KW - Western Tethys

U2 - 10.1016/j.gloplacha.2022.103811

DO - 10.1016/j.gloplacha.2022.103811

M3 - Article

VL - 212.2022

JO - Global and Planetary Change

JF - Global and Planetary Change

SN - 0921-8181

IS - May

M1 - 103811

ER -