Isotopic signals from Callovian–Kimmeridgian (Middle–Upper Jurassic) belemnites and bulk organic carbon, Staffin Bay, Isle of Skye, Scotland

Abstract

The stable isotope data presented here significantly extend and expand upon previous isotopic investigations of the Middle to Late Jurassic interval. The belemnite samples collected from the Staffin Bay and Staffin Shale formations from the Isle of Skye, Scotland, yielded oxygen isotope values consistent with Callovian-Kimmeridgian palaeotemperatures of 6.7-20.6 8C. The carbon isotope data comprise one of the first moderately high-resolution investigations of the relationship between terrestrial ä 13 C org (predominantly fossil wood debris) and marine ä 13 C carb (belemnites) as derived from a geologically coeval record. The Staffin Bay data reveal a broad Early to Mid-Oxfordian positive carbon isotope excursion. The excursion maximum occurs in the cordatum Zone (British Boreal ammonite zonation), although high values persist into the tenuiserratum Zone. The correspondence between the marine and terrestrial records indicates a strong coupling of the ocean-atmosphere system and suggests that the total exchangeable carbon reservoir would have been affected at this time. The Mid-Oxfordian negative carbon isotope excursions identified in published Tethyan records and commonly attributed to methane release are not recorded in the Staffin Bay data, which may suggest that the Tethyan excursions do not represent fluctuations in the global carbon reservoir and that the fidelity of the methane hypothesis should be re-evaluated.

Thermal maturity, hydrocarbon potential and kerogen type of some Triassic–Lower Cretaceous sediments from the SW Barents Sea and Svalbard

“…In this context, it was concluded that the Callovian-Oxfordian positive and the Middle Volgian negative 13 C org excursions and the Kimmeridgian-Middle Volgian negative trend for the investigated Middle Jurassic-Lower Cretaceous Agardhfjellet Formation are consistent with several other anomalies reported from elsewhere in the Boreal realm (e.g. Hammer et al, 2012;Katz et al, 2005;Nunn et al, 2009;Padden et al, 2002;Zakharov et al, 2014) and therefore reflect a global event.…”

The age of the Tojeira Formation (Late Jurassic, Early Kimmeridgian), of Montejunto, west-central Portugal

“…MS magnetic susceptibility carbonate carbon in the Tethyan realm and organic carbon in the Boreal realm. Boreal realm organic carbon records from age equivalent sections in the UK (Morgans-Bell et al 2001), Scotland (Nunn et al 2009) and Russia (Riboulleau et al 1998;Price and Rogov, 2009) show a conspicuous positive excursion in the R. cymodoce Zone (Sub-boreal equivalent to the S. platynota/A. hypselocyclum zones) and are correlated here to the Tojeira-1 section C-isotope record (Fig.…”

“…4). Likewise, from the Isle of Skye, Scotland, there is a peak in the C-isotope record in the R. cymodoce Zone (Nunn et al 2009), and in the carbonate carbon record for Makariev village, Russia, is a definitive positive peak (Riboulleau et al 1998;Price and Rogov, 2009). The cyclostratigraphical age suggestion for the Tojeira-1 section (constrained by biostratigraphy) places a conspicuous peak of similar scale to those Boreal records outlined, in the early A. hypselocyclum Zone.…”

“…This minor excursion is present in both the organic and carbonate carbon records from Scotland, as a positive fluctuation in the R. cymodoce Zone (Nunn et al 2009). However, as shown by an overlay of d 13 C carb Tethyan records of southern Europe by Price et al (2016), a minor positive peak in the A. hypselocyclum Zone is not clearly recognisable.…”

Carbon cycle history through the Jurassic–Cretaceous boundary: A new global δ13C stack

“…Likewise a declining marine δ 13 C org trend is seen in DSDP site 534A data reported by Falkowski et al (2005) from the Tithonian, before a pronounced positive event is seen associated with the Valanginian (Patton et al, 1984). Those Late Jurassic and Early Cretaceous δ 13 C org data derived from woody material and charcoal (Nunn et al, 2009(Nunn et al, , 2010Pearce et al, 2005;Gröcke et al, 2005) also reveal a long-term decline in carbon-isotopes through the Late Jurassic and a positive Valanginian excursion closely matching the marine carbon-isotope curves. Notably a lack of data is apparent for the latest Tithonian and earliest Berriasian.…”