Mid-Cretaceous floras and climate of the Russian high Arctic (Novosibirsk Islands, Northern Yakutiya)

Abstract

Two mid-Cretaceous floras collected in terrigenous and volcaniclastic deposits of the Novosibirsk Islands in the Russian high Arctic were studied. These floras are the most poleward mid-Cretaceous floras known and existed at palaeolatitudes up to 82–85° N. These represent our best insight into polar conditions at one of the warmest intervals in Earth history. An Albian flora from the Balyktakh Formation of the Kotel'nyi Island comprises 40 species of ferns, bennettites, cycadophytes, ginkgoaleans, czekanowskialeans, conifers and gymnosperms incertae sedis. This flora is most similar to the Albian Buor-kemuss Flora widespread in the Arctic Siberia and Alaska and, to a lesser extent, to the Aptian Silyap Flora of Siberia. A Turonian flora from the Derevyannye Gory Formation on the Novaya Sibir' Island includes approximately 50 taxa of ferns, ginkgoaleans, conifers and angiosperms. This flora exhibits plants common for the early Cretaceous as well as taxa typical for Cenomanian–Senonian, which implies that the age of the plant-bearing deposits is likely to be Turonian. The Cretaceous climate has often been described as ‘warm’ with a higher degree of equability than today with the near-polar regions in particular being much warmer than today. Our estimates using CLAMP and a new global gridded climate calibration demonstrate that for the Turonian Novaya Sibir' Flora plant physiognomy reflects a humid climate with warm summers and mild frost-free winters: the mean annual temperature is estimated to have been + 9.2 ± 2.2 °C, the warm month mean temperature + 17.2 ± 2.8 °C, the cold month mean temperature + 1.1 ± 3.8 °C and the mean growing season precipitation 537 ± 392 mm. These temperature parameters indicate that within 900 km of the Turonian North Pole the climate was similar to that of modern temperate, or even warm-temperate, zones but must have differed considerably in having pronounced high-latitude sunlight seasonality. The ecology of the late Cretaceous Arctic plants reflects their adaptation to this climate. Synchronous shedding of foliage (deciduousness) was by far the most common strategy and retention of leaves year round (evergreenness) was also viable for a small number of taxa. Large deciduous leaves typical for the Cretaceous Arctic dicots probably reflect the combination of a warm and humid climate with high-latitude light regime: long days in summer and predominance of relatively weak and mostly diffuse sunlight. The large range of leaf size in a given plant species of Arctic angiosperms was most probably linked to the seasonal character of annual shoot development.