EXPLORING THE ROLE OF MID-CRETACEOUS CARBON CYCLING ON FLOWERING PLANT RADIATION: AN INTEGRATED APPROACH FROM THE NON-MARINE SEDIMENTS OF WEST GREENLAND

Cretaceous carbon cycling was dynamic, evidenced by occurrences of widespread marine black shale deposited during oceanic anoxic events. OAEs were likely caused by rapidly increased atmospheric CO₂ triggering climatic and oceanographic feedbacks that led to massive organic-rich carbon burial. However, there are few high-resolution pCO₂ records across these events, despite their frequency in the Cretaceous. Studies have also revealed the angiosperms rapidly diversified during this period, and may have attained ecological dominance in phases to the detriment of other floral groups. We explore the relationship between OAE-associated carbon-cycle disturbances and angiosperm radiation in the context of the CO₂ starvation hypothesis, which proposes intervals of reduced atmospheric pCO₂ forced selection of angiosperous traits. The acquisition of such traits, which maximise photosynthesis under a declining CO₂ regime, is relatively well temporally constrained but our understanding of coeval changes in atmospheric pCO₂ is less established, particularly in relation to proposed CO₂ draw down during an OAE.

We aim to generate high-resolution pCO₂ records spanning mid-Cretaceous OAEs using the stomatal density method on fossil leaf cuticle from non-marine sediments of the Nuussuaq Peninsula, West Greenland. These fluvio-deltaic and lacustrine deposits have been known to contain well-preserved fossil flora since the collections of Oswald Heer (1870’s), and extensive work by Austin Boyd formed the basis of our field strategy. Carbon-isotope stratigraphy, generated from fossil wood and bulk organic matter, provides a refined age definition of the sediments exposed along the north coast of the peninsular. In agreement with previous palynological estimates, our data indicate the exposed Kome Formation is no older than earliest Albian, and a positive carbon-isotope excursion within the formation is probably correlative to OAE1b. The combination of macrofossil floral assemblages and our carbon-isotope stratigraphy suggests the Ravn Kløft Member of the Atane Formation likely spans the Albian–Cenomanian boundary (OAE1d). We provide the stomatal investigation results with respect to pCO₂ and demonstrate the excellent fossil preservation to reconstruct other aspects of terrestrial palaeoenvironments.