Palaeoclimatic conditions in Central Iberian Peninsula in the Senonian epoch (c. 72 mya) as inferred by pyrolysis compound specific isotopic analysis (Py-CSIA) of the fossil conifer (Frenelopsis oligostomata)
Frenelopsis oligostomata (FR) is an extinct Cretaceous conifer adapted to severe water stress. Well preserved fossil remains found in marls from the Upper Cretaceous (Senonian c. 72 Mya) in Guadalix de la Sierra (Madrid, Spain) (Almendros et al. 1982) are studied using stable isotope analysis in bulk (C, H, O, N IRMS) and in specific compounds released by pyrolysis (C, H, Py-CSIA). Stable isotopic analysis of bulk samples was carried out in a Thermo-Scientific Flash 2000 HT coupled to a Delta V Advantage IRMS. Compound specific isotopic analysis (Py-CSIA) was conducted with a Frontier Labs Pyrolyzer (3030D) attached to a Trace GC Ultra chromatograph with a GC-Isolink System and via a ConFlo IV to a Delta V IRMS. Chemical structure of compounds was inferred by comparing classical electron impact mass spectra from Py-GC/MS with Py-GC/FID and Py-GC/IRMS chromatograms under the same GC conditions. Heavy bulk ¿13C values were found (-20.5±0.02 ¿) pointing to a depleted stomatal conductance and FR paleoenvironmental growth conditions of water and salt stress. Values obtained for ¿D (-101.9±2.2 ¿), ¿15N (10.7±0.2 ¿) and ¿18O (20.9±0.39 ¿) lay within those previously reported for fossil floras growing in warm environment and probably with very high evaporation rates. We were able to obtain ¿13C signatures for a number of biogenic compounds released by pyrolysis from FR (Py-CSIA including polysaccharides, lipids (Fig. 1 left), lignin methoxyphenols and altered lignin (alkyl benzenes and alkylphenols). Plant-air C fractionation in compounds derived from altered lignin for a C3 photosystem plant is c. ¿13C¿ 20.0 ¿ and considering a fractionation (c. ¿13C¿ ¿3.0 ¿) due to the plant depleted stomatal conductance conditions, we estimate that the atmospheric ¿13C value in the area during the Senonian epoch in c. ¿13C = ¿5.3±0.2 ¿. This indicates that FR grew on a 13C enriched atmosphere that could be caused by emissions of 13C to the atmosphere from warm and acidified oceans by volcanic depositions and/or net terrestrial C uptake with selective removal of light 12C isotope by plants. Also we were able to measure ¿D for alkyl series in the range C24¿C29 (¿D = ¿124.44±5.2¿) (Fig. 1 right). This value was taken as a proxy to infer the H isotopic signal of water in the area in the Upper Cretaceous, giving a value for palaeowater ¿D = ¿24.44±5.2¿. This indicates that 75 Mya our plant probably uptake deuterium enriched rain water that again points to warm growing environmental conditions.
| Main Authors: | , , , , , |
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| Format: | comunicación de congreso biblioteca |
| Published: |
Centre national de la recherche scientifique (France)
2016-05-09
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| Online Access: | http://hdl.handle.net/10261/159805 |
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