Carbon‐Cycle Perturbation in the Middle Jurassic and Accompanying Changes in the Terrestrial Paleoenvironment

Abstract

Abstract Carbon‐isotope analyses of fossil wood from the Middle Jurassic Ravenscar Group, Yorkshire, NE England, reveal a significant excursion toward light isotopic values (δ13C change of −3 to −4‰) at about the Aalenian‐Bajocian boundary (∼174 Ma). A positive carbon isotopic excursion is also shown for the middle Bajocian (∼170 Ma) but is less clearly defined. These isotopic patterns are very similar to the few published marine carbonate records available for this time, in particular one based on belemnites from the Hebrides basin, NW Scotland, and others from pelagic limestones in Italy. The similarity of the terrestrial and marine isotope curves is an indication that the observed isotopic signal is a global phenomenon. Through parts of the Ravenscar Group (the Scarborough Formation), supplementary data from bulk organic carbon and palynofacies analysis confirm that isotopic curves based on bulk analyses may be strongly influenced by the balance of terrestrial versus marine organic matter present in th...