Earliest Jurassic plant assemblages from Sweden reveal a low-diversity ginkgoalean and cheirolepid flora dominating the post-extinction landscape.

Abstract

Background and aims: Rich Triassic-Jurassic plant assemblages from Skåne, southern Sweden, have been documented extensively over the past two centuries. However, no macrofloras from the lowermost part of the Helsingborg Member (Lower Jurassic) have been forthcoming and thus the age of the successions has not been well-constrained. Here we systematically describe and assess the palaeoecology and age of a newly discovered flora from the Boserup beds at Norra Albert Quarry, Skåne.

Methods: Plant macrofossils were examined using macrophotography, fluorescence microscopy, and scanning electron microscopy (SEM). Palynological analysis of the strata hosting the macroflora contributed to the palaeoenvironmental interpretations and refined the age of the deposits.

Results: The low-diversity post-extinction recovery forests of the earliest Jurassic were dominated by ginkgoopsids, cheirolepid conifers, and ferns, growing under seasonal mesothermal conditions. Dispersed charcoal indicates wildfires were present in the landscape at this time.

Conclusions: Despite the poor preservation of the fossils, the Boserup beds flora provides a window into vegetation recovery in the immediate aftermath of the end-Triassic extinction event. Initial recovery is characterised by the presence of needle- and scale-leafed seed plants (notably czekanowskialeans and Brachyphyllum producing Classopollis), along with a range of ground ferns.