Palynostratigraphy of the Triassic–Jurassic transition in southern Sweden

Abstract

Palynological samples from Upper Triassic and Lower Jurassic exposures and borehole sections of the Höganäs and Rya formations (Fm), NW Skåne (Sweden), exhibit diverse and generally well-preserved palynomorph assemblages that can be divided into four miospore zones (from bottom to top): (1) the informal “Topmost upper Rhaetian” zone of Lund; (2) the TSI assemblage zone which spans the Triassic–Jurassic (T–J) boundary; (3) the Hettangian Pinuspollenites–Trachysporites Zone and (4) the Sinemurian Cerebropollenites macroverrucosus Zone. Uppermost Rhaetian and T–J boundary strata have previously been considered to be absent in Skåne, but are identified palynologically in all but one (Kulla-Gunnarstorp) section in this study. The palynological assemblages characterise continental deposition with intermittent marine influences. The presence of well-preserved miospores in nearly all assemblages indicates minimal transport during dispersal and deposition. The T–J transition is characterised by a spore-spike, not previously recognised in T–J assemblages of Skåne. However, the upper Hettangian and Sinemurian assemblages of this study are similar in composition to coeval palynofloras derived from sediments deposited in paralic environments elsewhere in Skåne and Denmark.