A quantitative comparison of dispersed spore/pollen and plant megafossil assemblages from a Middle Jurassic plant bed from Yorkshire, UK

Abstract

Abstract.-Detailed quantitative data has previously been collected from plant megafossil assemblages from a Middle Jurassic (Aalenian) plant bed from Hasty Bank, North Yorkshire, UK. We conducted a similar analysis of palynological dispersed sporomorph (spore and pollen) assemblages collected from the same section using the same sampling regime: 67 sporomorph taxa were recorded from 50 samples taken at 10 cm intervals through the plant bed. Basic palynofacies analysis was also undertaken on each sample. Both dispersed sporomorph and plant megafossil assemblages display consistent changes in composition, diversity (richness), and abundance through time. However, the dispersed sporomorph and plant megafossil records provide conflicting evidence for the nature of parent vegetation. Specifically, conifers and ferns are underrepresented in plant megafossil assemblages, bryophytes and lycopsids are represented only in sporomorph assemblages, and sphenophytes, pteridosperms, Caytoniales, Cycadales, Ginkgoales and Bennettitales are comparatively underrepresented in sporomorph assemblages. Combined multivariate analysis (correspondence analysis and nonmetric multidimensional scaling) of sporomorph occurrence/abundance data demonstrates that temporal variation in sporomorph assemblages is the result of depositional change through the plant bed. The reproductive strategies of parent plants are considered to be a principal factor in shaping many of the major abundance and diversity irregularities between dispersed sporomorph and plant megafossil data sets that seemingly reflects different parent vegetation. Preferential occurrence/preservation of sporomorphs and equivalent parent plants is a consequence of a complex array of biological, ecological, geographical, taphonomic, and depositional factors that act inconsistently between and within fossil assemblages, which results in notable discrepancies between data sets.

Megaspores from the Lower Jurassic (Pliensbachian) Rotzo Formation (Monti Lessini, northern Italy) and their palaeoenvironmental implications

“…The megaspore record reveals, thus, a greater diversity of plants than the macrofossils alone. A similar abundance and diversity in the megaspore but near lack in megafossil record in the same deposit have already been observed from the Middle Jurassic of Yorkshire (Harris 1961;Slater and Wellman 2015).…”

Middle Jurassic vegetation dynamics based on quantitative analysis of spore/pollen assemblages from the Ravenscar Group, North Yorkshire, UK

“…Generalized geological map of the North Yorkshire coast. Modified from Milsom and Rawson (); Mjøs and Prestholm (); Palliani and Riding (); Rawson and Wright (); Slater and Wellman (); Slater et al . ().…”

“…Subdivisions of the Middle Jurassic of Yorkshire, marine units shaded. Modified from Rawson and Wright (); Slater and Wellman (); Slater et al . ().…”

“…Palaeofloristic reconstructions from these deposits rely primarily on plant megafossil assemblages (e.g. Spicer and Hill ), and although several dispersed sporomorph investigations have been carried out (Couper ; Chaloner ; Chaloner and Muir ; Riding and Wright ; Boulter and Windle ; Hubbard and Boulter ; Srivastava ; Slater and Wellman ), much of this work has focused on taxonomy and biostratigraphy (Couper ; Riding and Wright ; Srivastava ). This study aimed to build upon previous investigations into the palaeoflora of the Middle Jurassic using sporomorphs (e.g.…”

The Triassic to Early Jurassic palynological record of the Tarim Basin, China

“…The commonly used Bray-Curtis dissimilarity metric was used (e.g. Harrington 2008;Slater and Wellman 2015;Slater and Wellman 2016), and repeated runs were carried out for two dimensions until a convergent solution was established. NMDS was carried out in PAST (Hammer et al 2001) using relative abundance (percentage) data.…”