Palynological and geochemical assessment of the Late Triassic in the high-latitude section of Festningen (Svalbard)

Abstract

The Late Triassic (237-201.4 Ma) is characterized by several biotic turnovers and carbon isotope perturbations, commonly linked to large-scale volcanism. In order to examine the extent of volcanic-induced kill mechanisms, records from high-latitude sites are required to assess the global impact on the biosphere, as most data has been recorded in mid-latitude sites in NW Europe. To this end, the floral turnovers and geochemical perturbations of an Upper Triassic succession are examined from a high-latitude section at Festningen (Svalbard). The Festningen section contains vertical sedimentary outcrops continually exposing from the Upper Carboniferous to Palaeogene. Contradicting biostratigraphic age interpretations have been put forth in studies on the Upper Triassic Knorringfjellet Formation (Wilhelmøya Subgroup). Here, palynological and geochemical (carbon) examinations are presented which identify floral trends and carbon cycle perturbations that indicate environmental disturbances. A new stratigraphic framework is constructed based on palynomorph content. In addition, thin sections of phosphate rich beds were investigated from the lower Knorringfjellet Formation.

The dinoflagellate cyst dominated lower interval of the Knorringfjellet Formation is of a Norian age and seems to reflect an Arctic circumpolar correlative event. In the upper interval of the Knorringfjellet Formation the apparent occurrence of the Jurassic marker species Cerebropollenites thiergartii (recently recombined as Sciadopityspollenites thiergartii) together with abundant Triassic marker species results in divergent age interpretations. Here, a Rhaetian age is proposed for this interval, as C. thiergartii is occasionally reported in the Rhaetian and its first occurrences vary between localities. The results cast further doubt on the reliability of C. thiergartii as a marker for the base of the Jurassic. Similar reports of C. thiergartii in Triassic assemblages in northern Norway might indicate the taxa originated in high-latitude regions.

Phosphatic coated grains identified in the Norian phosphate rich beds indicate disturbed anoxic conditions, possibly linked to intensified oceanic upwelling resulting from climate warming. This bed could be correlated to temperature peaks around the Carnian-Norian boundary or to the mid-late Norian Angayucham LIP, as dating is not very precise. Vegetational reconstruction reveals a mire landscape dominated by ferns and cycads/ginkgos, with conifers prevailing in drier areas. In the lower Rhaetian interval an increase in xerophytic taxa might indicate a period of relatively drier conditions. No spore spikes indicating environmental disturbance were found. A decrease in dinocysts coinciding with a foraminiferal discontinuity indicates a marine turnover during the Rhaetian. A CIE possibly correlated to the precursor CIE, or an earlier Rhaetian carbon cycle perturbation, is recognized at the top of the interval analysed in this study.