Early to Middle Jurassic palaeoenvironmental changes: High resolution δ13C and δ18O records from the UK

TY - ABST

T1 - Early to Middle Jurassic palaeoenvironmental changes: High resolution δ13C and δ18O records from the UK

AU - Korte, Christoph

AU - Hesselbo, Stephen

AU - Ullmann, Clemens Vinzenz

AU - Ruhl, Micha

AU - Thibault, Nicolas Rudolph

PY - 2013

Y1 - 2013

N2 - Low-Mg-calcite fossils, such as bivalves, belemnites and brachiopods, and bulk rocks have been extensively utilized to reconstruct past seawater chemistry and paleoenviron¬mental changes. Recent work on major bioevents demonstrated that particularly higher resolution stable isotope records are necessary to reveal short-term paleoenviron¬mental fluctuations and, in addition, to discover its causes. Here we present a new high resolution carbon and oxygen isotope dataset generated from low-Mg-calcite fossils, fossil wood and bulk rocks collected from Early to Middle Jurassic marine successions of the UK. In addition to the well know carbon isotope fluctuations across the Toarcian Oceanic Anoxic Event (OAE), further δ13C perturbations have been obtained from the analyzed samples: (1) a positive trend in the earliest Sinemurian (Conybeari zone), negative excursions in the (2) Sinemurian Bucklandi zone and (3) at the Sinemurian-Pliensbachian boundary (upper raricostatum and lower jamesoni zones), and (4) a positive excursion in the Late Pliensbachian margaritatus zone. At the Sinemurian-Pliensbachian boundary a positive δ18O shift occurs during the negative δ13C excursion, suggesting most likely bottom water cooling as a result of the Early Pliensbachian transgression. Two additional cooling events, (1) in the Late Pliensbachian and (2) during the Aalenian-Bajocian, are discovered by positive oxygen isotope trends. The cool Late Pliensbachian shallow sea-floor is in agreement with previous inference of partial icehouse conditions at that time. More uncertain are potential icehouse interludes during the Aalenian-Bajocian interval. The new isotope datasets show partly a strong similarity between the positions of the global warming/cooling events within transgressive/regressive phases of second-order depositional sequences though the Early to Middle Juras¬sic supporting the idea that second-order depositional se¬quences are a result of eustatic sea-level changes at that time.

AB - Low-Mg-calcite fossils, such as bivalves, belemnites and brachiopods, and bulk rocks have been extensively utilized to reconstruct past seawater chemistry and paleoenviron¬mental changes. Recent work on major bioevents demonstrated that particularly higher resolution stable isotope records are necessary to reveal short-term paleoenviron¬mental fluctuations and, in addition, to discover its causes. Here we present a new high resolution carbon and oxygen isotope dataset generated from low-Mg-calcite fossils, fossil wood and bulk rocks collected from Early to Middle Jurassic marine successions of the UK. In addition to the well know carbon isotope fluctuations across the Toarcian Oceanic Anoxic Event (OAE), further δ13C perturbations have been obtained from the analyzed samples: (1) a positive trend in the earliest Sinemurian (Conybeari zone), negative excursions in the (2) Sinemurian Bucklandi zone and (3) at the Sinemurian-Pliensbachian boundary (upper raricostatum and lower jamesoni zones), and (4) a positive excursion in the Late Pliensbachian margaritatus zone. At the Sinemurian-Pliensbachian boundary a positive δ18O shift occurs during the negative δ13C excursion, suggesting most likely bottom water cooling as a result of the Early Pliensbachian transgression. Two additional cooling events, (1) in the Late Pliensbachian and (2) during the Aalenian-Bajocian, are discovered by positive oxygen isotope trends. The cool Late Pliensbachian shallow sea-floor is in agreement with previous inference of partial icehouse conditions at that time. More uncertain are potential icehouse interludes during the Aalenian-Bajocian interval. The new isotope datasets show partly a strong similarity between the positions of the global warming/cooling events within transgressive/regressive phases of second-order depositional sequences though the Early to Middle Juras¬sic supporting the idea that second-order depositional se¬quences are a result of eustatic sea-level changes at that time.

M3 - Conference abstract for conference

T2 - AGU Fall meeting 2013

Y2 - 9 December 2013 through 13 December 2013

ER -