Cretaceous pCO 2 estimation from stomatal frequency analysis of gymnosperm leaves of Patagonia, Argentina

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Stomatal frequency of fossil conifers and ginkgoals cuticles were considered as potential indicators of the pCO 2 values in the Patagonian palaeoatmosphere during the Cretaceous. Samples are from continental deposits of early Upper Aptian age (Anfiteatro de Ticó and Punta del Barco formations) and Upper Albian–Lower Cenomanian age (Kachaike Formation), both outcropping in Andean and extra-Andean portions of Santa Cruz province, Argentina. It can be inferred that the CO 2 atmospheric content was similar during both stages, or was slightly higher toward the Late Albian–Early Cenomanian. The CO 2 content estimated from the conifers is between ~ 700 and 1400 ppmv (or lower from the mid-Aptian ginkgoals). This CO 2 range is consistent with those predicted worldwide by previous studies (stomatal indices, biogeochemical models and carbon isotopes), and implies a CO 2 content 2.3–4.0 times higher than present. The high atmospheric CO 2 content during the Middle Aptian and Late Albian–Early Cenomanian was probably linked to a warming process at high latitudes during these times. This is consistent with the floristic development recorded during both stages in Patagonia.