Late Cretaceous climate signal of the Northern Pekulney Range Flora of northeastern Russia

Plant-bearing continental deposits from the northern Pekulney mountain range in the Anadyr-Koryak subregion of northeastern Russia (approximately 66°N, 175°E) represent a rich and diverse flora growing close to the Late Cretaceous North Pole at a palaeolatitude of ∼78°N. The Early Coniacian age of this flora is based on biostratigraphic correlation of the plant-bearing beds with underlying and overlying marine units. The Northern Pekulney Range Flora comprises two large plant macrofossil assemblages, one from the Tylpegyrgynai Formation on the western slopes of the northern Pekulney Range and the other from the Poperechnaya Formation on its northeastern slopes. The flora is dominated by angiosperms followed by conifers, ferns, cycadophytes, ginkgophytes and sphenophytes, in decreasing order of species diversity. Dicotyledonous angiosperm leaves (57 morphotypes) from the Northern Pekulney Range Flora were subjected to a Climate Leaf Analysis Multivariate Program (CLAMP) physiognomic analysis. Separate analyses of the constituent assemblages from the Tylpegyrgynai and Poperechnaya formations yielded 27 and 39 morphotypes, respectively. Results suggest that the Northern Pekulney Range Flora experienced a mean annual temperature of 8.1±1.2 °C, a cold month mean temperature of −1.5±1.9 °C, a mean monthly growing season precipitation of 78.8±36.9 mm and a growing season of 5.3±0.7 months. This suggests a warm temperate climate lacking pronounced drought, in which the polar light regime constrained the length of the growing season. CLAMP results for the Tylpegyrgynai Formation Flora suggest slightly higher temperatures, with a mean annual temperature of 9.4±1.2 °C and a cold month mean temperature of 0.9±1.9 °C, whilst estimates for the Poperechnaya Formation Flora are cooler, with a mean annual temperature of 7.3±1.2 °C and a cold month mean temperature of −2.7±1.9 °C. Because the floras from the Tylpegyrgynai and Poperechnaya formations also exhibit differences in their taxonomy and physiognomy, they should be considered as two distinct floras. The overall taxonomic composition of these floras, their foliar physiognomy and estimated palaeoclimate parameters suggest a deciduous phenology with a few evergreen elements. Comparisons with other Arctic Coniacian floras are consistent with the high latitudinal position of the Northern Pekulney Range Flora and its proximity to the northern proto-Pacific Ocean.