The relationship of plant leaf δ13C-alkanes and salinity in coastal ecosystems applied to palaeobotany: Case study from the Cenomanian of the Bohemian Cretaceous Basin, Czechia

Petra Zahajská, Jana Čepičková, Jakub Trubač, Nikolai Pedentchouk, Jiří Kvaček

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Abstract

Stable carbon isotopes in fossil leaf cuticles (n-alkanes, δ 13C n−alkanes) extracted from the sediment are widely used for palaeoenvironmental reconstructions. This approach relies on a series of assumptions (such as the plant-group-specific isotopic range, or the atmospheric CO 2 being the major factor for the isotopic values) and leaves out the complexity of the carbon isotope fractionation within the plant through time, space, and different environments. The leaf cuticle is a unique archive of local environmental conditions, which has the potential to constrain individual plant habitat. To explore the applicability of the information gained from the δ 13C n−alkanes from fossil plants, a fossil coastal environment was studied. During the Cenomanian (100.5–93.9 Ma), the basal part of the Bohemian Cretaceous Basin, including locality Pecínov (Czechia), was formed as a result of sea transgression to the Palaeozoic Bohemian Massif triggered by the Alpine orogenesis. Coastal halophytic vegetation growing in this zone of prograding sea has no extant equivalent, and there are uncertainties associated with vegetation distribution or individual taxa habitat. Therefore, we examine the relationship between δ 13C n−alkanes extracted from individual leaves of coastal C3 plants (fossil and modern) and osmotic stress (salinity and drought) to reconstruct the individual plant habitat, thus, vegetation distribution in the coastal zone. We investigated modern mangrove and salt marsh vegetation in New Zealand and the United Kingdom, respectively, as well as transition zones (mangrove invading original salt marshes) for δ 13C, soil moisture and salinity to build a calibration of the relationship, which is then applied to the Cenomanian fossil leaves from the locality of Pecínov. We found a positive correlation between water stress (caused by salinity or drought) and the δ 13C values of n‐C 25, n‐C 27, n‐C 29 and n‐C 31 alkanes when combining all species from all modern localities. However, the absence of a strong correlation within individual species suggests a combination of several factors controlling the carbon isotopic composition. Nevertheless, the general response of δ 13C to osmotic stress can be applied to compare the habitat of modern and fossil coastal plants. Thus, by using this relationship, we reconstructed the relative salinity and water stress of individual species of the Cenomanian plants by relating them to modern species-specific ranges of n‐C 29 isotopic signatures. We showed that the δ 13C n−alkanes of fossil plant cuticles/leaves can be a valuable tool in the reconstruction of plant habitat and help us understand evolution of fossil environments in time and space. Additionally, our data further confirm that the δ 13C acquired from plants should be used with caution when reconstructing global atmospheric CO 2 because the osmotic stress can shift the δ 13C in plants growing in terrestrial environments, particularly in coastal sea-influenced ecosystems.

Original languageEnglish
Article number112052
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume638
Early online date24 Jan 2024
DOIs
Publication statusPublished - 15 Mar 2024

Keywords

  • Carbon isotopes
  • Coastal environment
  • Leaf waxes
  • Osmotic stress
  • Salinity
  • The Cenomanian

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