Shallow marine carbon and oxygen isotope and elemental records indicate icehouse‐greenhouse cycles during the Early Jurassic

Abstract

For much of the Mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences. We present a carbon and oxygen isotope and elemental record for part of the Early Jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the Cleveland Basin, UK. The invertebrate isotope record is supplemented with carbon isotope data from fossil wood, which samples atmospheric carbon. New data elucidate two major global carbon isotope events, a negative excursion of ∼2‰ at the Sinemurian–Pliensbachian boundary, and a positive excursion of ∼2‰ in the Late Pliensbachian. The Sinemurian–Pliensbachian boundary event is similar to the slightly younger Toarcian Oceanic Anoxic Event and is characterized by deposition of relatively deepwater organic‐rich shale. The Late Pliensbachian strata by contrast are characterized by shallow marine deposition. Oxygen isotope data imply cooling locally for both events. However, because deeper water conditions characterize the Sinemurian–Pliensbachian boundary in the Cleveland Basin the temperature drop is likely of local significance; in contrast a cool Late Pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions. Both the large‐scale, long‐term and small‐scale, short‐duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy. Isotope events and the sea level cycles are concluded to reflect processes of global significance, supporting the idea of an Early Jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 Ma.

Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)

“…6). The Late Sinemurian positive CIE was also recorded in the Cleveland Basin of the UK by Korte and Hesselbo (2011) and in the δ 13 C org data of the Wessex Basin of southern UK by Jenkyns and Weedon (2013).…”

“…Similarly, the δ 13 C bel curve obtained by Quesada et al (2005) in the neighbouring Basque-Cantabrian Basin shows the presence of a negative CIE in a similar stratigraphical position. In the Cleveland Basin in the UK, the studies on the SinemurianPliensbachian deposits conducted by , Jenkyns et al (2002) and Korte and Hesselbo (2011) reflect the presence of this Early Pliensbachian δ 13 C bel decrease in values. In the Peniche section of the Lusitanian Basin of Portugal, this negative CIE was also recorded by Suan et al (2010) in brachiopod calcite, and in bulk carbonates in Italy (Woodfine et al, 2008;Francheschi et al, 2014).…”

“…The magnitude of approximately 1.5-2 ‰ of this negative excursion appears to be quite consistent across the different European localities. Korte and Hesselbo (2011) pointed out that the Early Pliensbachian δ 13 C negative excursion seems to be global in character, resulting from the injection of isotopically light carbon from some remote source, such as methane from clathrates, wetlands, or thermal decomposition, thermal metamorphism or decomposition of older organic-rich deposits. However, none of these possibilities has yet been documented.…”

“…Nevertheless, with the exception of several sections (Rosales et al, 2004;Korte and Hesselbo, 2011;Suan et al, 2008Suan et al, , 2010, few data have been published on the evolution of seawater palaeotemperatures during the latest Sinemurian and the Pliensbachian, even some more papers studied the climatic changes of parts of the Late Pliensbachian and Early Toarcian (i.e. McArthur et al, 2000;Jenkyns et al, 2002;van de Schootbrugge et al, 2010;Gómez and Goy, 2011;Armendáriz et al, 2012;Harazim et al, 2013).…”

Optical and geochemical characterization of Upper Sinemurian (Lower Jurassic) fossil wood from the Lusitanian Basin (Portugal)

“…We found that the observed natural variation of δ 13 C posed many problems when analyzing our data because of a similar range of variation detected in our dataset, making it impossible to predict the direction of change (i.e., increasing or decreasing) of measured δ 13 C relative to the original wood carbon isotopic composition. The apparent dissimilarity of the obtained fossil wood record with contemporaneous data obtained from shells and fossil wood (Korte and Hesselbo, 2011) suggests that the δ 13 C of the studied samples does not reflect the δ 13 C of the paleoatmosphere. The organic petrographic observations and the positive correlation between TC and δ 13 C (Figs.…”