Late Jurassic-Early Cretaceous phytoplankton ecosystem evolution interrupted by the late Valanginian Weissert carbon isotope event

Abstract

The Late Jurassic-Early Cretaceous Phytoplankton Ecosystem Evolution and its associated Calcification Event were major evolutionary innovations of calcareous marine pelagic micro-organisms. Beginning about 160 Ma in the Oxfordian Stage calcareous nannofossils and calcareous dinoflagellates began calcifying their tests that subsequently accumulated as calcareous ooze. By the Tithonian Stage and continuing into the early Valanginian, calpionellids added to the diversification and expansion of this new pelagic ecosystem. This gradual, progressive ecosystem change in the oceanic photic realm was associated with increased burial of light carbon isotope. This calcareous plankton ecosystem suffered a crisis about 135 Ma by the late Valanginian Carbon Isotope Excursion. This isotope excursion was temporally related to emplacement of the Paraná-Etendeka LIP in the Paraná Basin in South America.

The upper Valanginian Carbon Isotope Excursion (VCIE) is a positive δ¹³C peak 1.5‰ to 3.0‰. In a thick terrigenous section, Japan, this excursion has four subunits bracketed by three radioisotope ages on ash beds. The VCIE began at 135.56 Ma and ended at 132.50 Ma. Its mean duration was 2.47 Myr. The VCIE subunits are correlated globally. Among these sections the age of the VCIE spans from 135.79 Ma to 132.25 Ma. 

The VCIE documents increased terrigenous sediment deposition and relative sea-level rise in the Gulf of Mexico, west-central Atlantic, France, Italy, and Oman. Globally, climate became more humid with lower atmospheric pCO₂ as subaerial volcanics were emplaced and weathered. Coincident was the late Valanginian Nannofossil-Calpionellid-Calcareous-Dinoflagellate Crisis characterized by decreased abundance and diversity of these three groups. The biotic crisis is related to the VCIE and changing paleoenvironmental processes. This study illustrates ocean-climate processes that affected the latest Jurassic-earliest Cretaceous Earth system.