EGU21-11778
https://doi.org/10.5194/egusphere-egu21-11778
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Fruit carbonate in Lithospermeae: 14C, stable isotope composition and potential as a paleoenvrionmental proxy

Konstantin Pustovoytov and Simone Riehl
Konstantin Pustovoytov and Simone Riehl
  • University of Tubingen, Institute for Archaeological Sciences , Germany (knpustov_les@mail.ru)

The tribe Lithospermeae (fam. Boraginaceae) represents one of very few taxa vascular plants that accumulate appreciable amounts of calcium carbonate in their tissues. The CaCO3 is localized in the pericarp sclerenchyma, which makes their small fruits (nutlets) mechanically durable and provides their good preservation in sediments and cultural layers. Fossil Lithospermeae fruits appear as whitish, slightly elongated entities, 3-5 mm in length.  At archaeological sites, the nutlets can be of diverse origin: in most contexts they represent carpological evidence for weed flora of the past, however, some findings suggest that they were used for decorative purposes (beads etc.).  

Here we overview the potential use of fruit carbonate of Lithospermeae in paleoecological research.   

14C-dating: Fruit carbonate of the taxon can be successfully dated with radiocarbon.  

The 14C concentration in the CaCO3 fraction of modern nutlets is well-correlated to the recent atmospheric 14C levels. Radiocarbon ages of old nutlets are in good correspondence with the age ranges of archaeological contexts. Obviously, fruit carbonate can represent a geochemically closed system for millennia in sediment environments.               

δ18O values: Our data based on an array of herbarium exemplars of Lithospermeae, suggest that the δ18O of fruit carbonate is distinctively sensitive to the amount of atmospheric precipitation during the warm season. The degree of correlation between δ18O and local air temperatures is lower.

We further performed an experiment on gromwell (Buglossoides arvensis (L.) I.M.Johnst), irrigated by water with different oxygen isotope signatures. The δ18O values of fruit CaCO3 showed correlation to the δ18O of irrigation water. The oxygen isotope fractionation in fruit carbonate turned out to be surprisingly low with 1000lnα = 4.72±3.49, which is relatively close to foraminiferal CaCO3.

 δ13C values: In contrast to the oxygen isotope signature, we did not find a strong correlation of the δ13C values of fruit carbonate to precipitation and temperature.  However, the photosynthetic origin of carbon in fruit CaCO3 admits a possibility of some links of δ13C to ambient factors.  

   

How to cite: Pustovoytov, K. and Riehl, S.: Fruit carbonate in Lithospermeae: 14C, stable isotope composition and potential as a paleoenvrionmental proxy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11778, https://doi.org/10.5194/egusphere-egu21-11778, 2021.

Corresponding presentation materials formerly uploaded have been withdrawn.