Environmental drivers of size changes in lower Jurassic Schizosphaerella spp

• Published in: Marine micropaleontology 2021-09, Vol.168, p.102053, Article 102053
• Main Authors: Peti, Leonie, Thibault, Nicolas, Korte, Christoph, Ullmann, Clemens V., Cachão, Mario, Fibæk, Marie
• Format: Article
• Language: English
• Subjects: Biometric study; Calcareous nannofossils; Multivariate statistics; Paris Basin; Sancerre-Couy; Stable isotopes
• ISSN: 0377-8398; 1872-6186
• DOI: 10.1016/j.marmicro.2021.102053

The Early Jurassic nannofossil Schizosphaerella has displayed major changes in its mean valve size through time. These variations are investigated in detail in the Sinemurian to lowermost Toarcian of the Sancerre-Couy core (Paris Basin), based on previously published measurements of 7050 specimens. Through multivariate morphon analysis and mixture analysis, we decipher three distinct overlapping varieties of Schizosphaerella (small, medium, large) and show that mean size changes of this taxon can be mostly related to variations in the relative abundance of these three varieties. Comparison to facies changes and to newly and previously acquired geochemical data (bulk carbonate C and O isotopes and organic C isotopes, %CaCO3 and TOC) suggest that, whilst sea-surface temperature was indeed an important driver of size changes in Schizosphaerella, it is insufficient on its own to explain the full variability of our dataset. Likewise, sea-level controlled proximal-distal variations and levels of nutrient supply were additional drivers of Schizosphaerella size changes. The small population of Schizosphaerella remains, however, a good indicator for warmer episodes. [Display omitted] •Schizosphaerella is composed of three pseudo-cryptic variants•The 3 variants strongly overlap and are only distinguishable by biometric studies•Sea-level and temperature are main drivers of Schizosphaerella size changes•Bulk δ18O matching global trends limited to late Pliensbachian