Palynological investigation of the Mid-Sinemurian (Early Jurassic) carbon cycle perturbation

Abstract

The region surrounding the Central European Basin during Early Jurassic age was marked by a remarkably stable period in terms of climate and vegetation. However, a recent study conducted in the UK uncovered a warming event in the Upper Sinemurian stage of the Early Jurassic. These new results, based on palynology and carbon isotope measurements, necessitate the gathering of more data from Sinemurian material from other sites for comparison, which is what this study seeks to accomplish. Roughly 60 meters of core material from the German Schandelah section was sampled in 1-meter intervals, and the resulting samples were processed to yield palynological slides. The resulting assemblages are characterised by a remarkable stability in terms of palynomorph taxa composition and abundance. The marine record is characterised by two acmes of the dinoflagellate cyst Liasidium variabile, in the Obtusum and Oxynotum ammonite zones of the Upper Sinemurian. In order to better quantitively asses these palynomorph records, a Sporomorph Ecogroup (SEG) model, and several SEG and palynomorph based proxies are used. Once more, records document rather stable vegetation developments, but variations in the Upland SEG group and spore/bisaccate (S/BP) ratio indicate the probable occurrence of relative sea level rise during intervals in the Lower and Upper Sinemurian (Semicostatum and Obtusum/Oxynotum ammonite zone, respectively). The apparent stability of the palynoflora contrasts with the report from the UK. The results of this study, and studies performed on other localities, makes the possibility of a global warming event during deposition of the Upper Sinemurian strata highly unlikely. The need for this interval to be studied outside of Europe is acknowledged, though, and definitive conclusions can only be made if a global database of palynological and stable isotope data is compiled. Until such research is conducted, the image of stable vegetation in the regions surrounding the Central European Basin during the Sinemurian still remains viable.